Help with a "D&D Generations" System

[Fuzzy Logic]

Basic premise: Rather than playing a single character, players are playing a family of adventurers over a long time period.

Extended Description: The Emporer of Shield city has discovered a dangerous demiplane which threatens his kingdom. He turns to a powerful artefact, the crown of the seven-headed cat, to solve this problem. The crown picks 7 adventurers to solve this problem. Once through the portal they conquer a small parcel of land around it and must defend the portal from the demiplanes denizens. This may take up to a thousand years.

How it works: After the founder generation, the players have less control over their character creation. Roll a D12 for class, as your child will not be guaranteed to follow in your footsteps. Race is the same as yours,
And starting equipment is divvied out from your families treasure hoarde. The crown drains the life force of the creatures around it and redistribute s it as it sees fit. What this means is long-lived races die on their 99th birthday, and player's characters will start with some fraction of their previous characters level or exp.

Where I need help: I would like to come up with a table of character options for my players to allow them to customise their characters at a cost. So the two I have so far are STERILE: the crown has secretly rendered you sterile and your character has to adopt, roll a new race. Cost= 1 level. STRICT PARENT: The crown forces your character to harshly control their child's upbringing, pick your class for your new character. Cost = 2 levels.
Neither of these are set in stone btw. I'm looking for a tense decision making process where you're never sure whether you should retire your character now to bank the XP and loot, or push on for just a bit longer. Ideas for the table, how to weight the cost of options on the table, or ways for characters to spend their gold ( spend 10,000 GP to build an alchemy lab that halve the cost of healing potions) are all welcome and very much appreciated. When it's done I'll edit this post and put it here for anyone to use. Thank you for reading, and thank you doubly if you decide to help!

[Shimeran]

I'm not sure those rules drive the kind of difficult decisions you seem to be looking for. For example, I'm seeing all that reason to retire early. In the event of a TPK, you'd lose any equipment on the party, but anything already banked back home should be safe. Does the xp transfer only happen if the character dies of old age / crown sacrifice? If not, then I'm not sure how they bank xp by retiring early.

The listed character options are also somewhat weird in that both leaving something up to chance (rolling for race) and avoiding doing so (picking classes) consume the same resource.

What I'd be more tempted to do for that tension is play up those aging penalties. Maybe the crown fixes aging to a set pace. For longer lived races, this grants mental maturity sooner at the cost of physical degradation where as for shorter lived races it stunts mental growth but preserves the body. That way the question becomes do you keep to the more experienced but aged older characters or switch to younger but less experienced folk. For extra oomph, consider either making aging harsher, such as the crown causing afflictions as they age, or giving older characters an edge in administration. You could also have children gain xp over time, decreasing the level gap. Putting funding toward guilds and training facilities could increase this rate, capped the levels of previous characters.

I'm also reconsider the table options. For example, allow adoption without specifying the character is sterile. Perhaps that's just an aging affliction instead. Then simply have each child cut into the household budget. That essentially makes each child a "reroll" for a potential heir, through at a monetary cost.

For class choice, maybe you could roll up a "passion" for each child when they reach a certain age. If their class choice lets them follow that passion, they might gain a small boon like an extra trait or xp boost. However, trying to force them into a class that doesn't fit their passion should trigger a backlash, such as gaining a drawback, xp loss, or them multiclassing into a class that meets their passion despite your wishes. I'd be tempted to make the backlash a roll so the effect varied between children. Promotional activities and events might allow a greater chance of a given passion, though at a cost.

[Fuzzy Logic]

These are excellent ideas, thank you so much! I knew something wasn't working but I figured it was not having enough ideas for the table. This way will work much better. Is anyone interested in these rules when I finish writing them up?

[Knaight]

Are you at all familiar with Pendragon? It has a lot of rules for exactly this, and they're worth looking over (I'd also suggest looking into Massive Chalice, but I suspect you have). Above and beyond that, here are some suggestions on bloodline traits in general to really get the familial line thing across. I'm working on the assumption that you want extensive codified rules here, so here goes:
Dynastic Effects
The bloodlines of adventuring dynasties are strong, and the traits of their heroic founders echo down the generations. In addition, as families grow only the best tend to become adventurers. Each generation down, the baseline for adventurers gets better. In addition as these dynasties retire the children grow up around skilled adventurers.
Attribute Generation
The traits of the founding generation may not apply to every member of a family, but there are some definite trends.

Every dynasty distributes 6 attribute generation points (AGP) between the attributes.
For each attribute, roll (3+AGP)d6, keeping the best 3. There is no swapping between attributes.
There are magic items, blessings, etc. that can permanently change a dynasty. These can give more AGP than would otherwise be given. Said items compete with those used by present characters, as they're rare and tend to require being built into expensive buildings.
Occasionally there are oddities in a family. Two attributes can be switched at character generation, at the cost of one level.
There are also generational shifts. An AGP can be permanently reassigned, at the cost of two levels.
Every so often a ruler will have a lot of children. They tend to receive less training as a result, but the best have more inborn talent, and they'll pass it down a generation. A new AGP can be added at the cost of ten levels.
Occasionally the opposite happens, with relatively few children. They'll be better trained, but the best are likely to be less talented. An AGP can be traded away, and five levels gained at start, to the maximum of the highest level retired adventurers.


Class Training
Retired but still living adventurers of an older generation train those younger than them, establishing a set of baselines. These baselines establish the options for new characters.

There is a Starting Total Level (SLt) and Starting Class Level (SLc) for each family.
SLt is equal to half the level of the highest level retired adventurer, or one, whichever is higher.
SLc is equal to the class level of the retired adventurer with the most class levels in a class, or one, whichever is higher.
Retired family members may be recused from training, and those recused are not counted when determining SLt or SLc.
These recused members may instead establish a dynastic tradition. Dynastic traditions take 15 years to establish, and mechanically count as retired adventurers for SLt and SLc determination - they're also more than a little expensive to establish.


Aging
Actual chronological age only counts for so much. Adventuring is a hard life, and adventurers age faster than more settled family members. This is even more true on a hostile demiplane where those adventuring are away from the protection of the crown.

Max age is set to 100 years for all races.
Adventurers are generally capable of adventuring at age 20. They can start younger than that, but at a -1 level penalty per year.
Each year adventuring ages an adventurer by two years. Years not adventuring age them by only one.
The age categories are standardized: Middle Age sets in at age 40, Old at 60, and Venerable at 80.
There are magic items which provide health and age resistance to the dynasty. These bump up the age breaks for middle age, old, venerable, and dead by 1, 2, 3, and 4 years respectively (Or larger increments of 4). They also get really expensive really fast.


The Compound
These dynasties need somewhere to live, and a given area can only support so many people. Once out of space excess people tend to make a trip through the portal to the homeland. Said portal is one way.

Every adventurer (retired or otherwise) requires support from a broader community. Each square mile of settled land can support one adventurer.
The demiplane is dangerous, and to keep the home compound reasonably safe requires fortifications. One small fortification per 10 square miles is reccomended, but there's room for flexibility on this ratio. Adjust encounter tables for home base attacks accordingly.
Each 10 square miles or so can usually support one non-fortress specialized building, in addition to all of the food production and similar.

[ideasmith]

My Scroll of Generations (https://dnd-wiki.org/wiki/User:Ideasmith#Scroll_of_Generations) articles might help; they are "A collection of rules to help with long time-skips between adventures". They can be found at:

https://dnd-wiki.org/wiki/User:Ideasmith#Scroll_of_Generations

[Zale]

Someone did a non-D&D based generational game way-back, here (http://www.giantitp.com/forums/showthread.php?394358-Dynasty-Multi-generational-civ-building-hero-adventuring-god-game)'s the thread for it if you want for inspiration.