A bit of help with a Wizard

[pbdr]

So, I am making a "retired" wizard to use in my campaign.

It' going to be an ex adventuring husband and wife, that have retired to a life of farming and contemplation (more contemplation than farming, think of the painting "American Gothic"). The pair have some important info and may be able to help the PCs with the second stage of the plot. (The first part of the plot is they are being hunted by a necromancer that wants to use them in a ritual to open a small locked demi plane/prison containing devils in the underdark. The second part will be the results of the "door" to the prison being weakened and devils start to do, well, devilish things. The "retired" couple helped forge the prison in the first place.)

The PCs will meet up with them at their farm (or be directed to it at some point) and it is likely the PCs will attack them (long story involving a Green Hag, but they distrust anyone that looks decrepit...).

My problem is that I'm not too experienced with spell casters. So, I'm looking for ideas. PCs will be about 10th lvl, the couple will be 15th - 17th. The wife will be a wizard (straight up or with a single PrC from core or FR), the husband will be a Druid or Cleric (i'm thinking cleric with magic and knowledge domains, because that will give the PCs a non-hostile source of raise dead in case of emergency later, which thy need because they haven't left many bridges unburned...).

What i'm looking for is how to shut the PCs down completely and non-violently if they attack. I.e. PC, "All right I grab/smack/shoot/ etc. the old man/woman". DM, "OK [blank] happens and you are all paralyzed/stunned/trapped in a globe of force". This couple will end up being a resource for the PCs, but I need to get across that they are not "XP and loot".....

MY ideas/specific questions. Contingency seem likely to be involved. Can I have a contingency that cast a time stop? What about a contingency to cast mass hold monster or power word stun?

Other ideas are welcome.

I'm limited to Core plus Faerun.

[AWiz_Abroad]

Sanctum Spelled Quickened Forcecage
Ditto Resilient Sphere

It would help to know your party composition, so we can plot around your party's likely saves/tactics.

[pbdr]

It want to use core and FR only for spells and feats (for the most part, I allow the PCs other materials by DM caveat, but tend not to use something the PCs don't) so no sanctum spell.

The party is a ranger, barbarian, warlock/beguiler, and NPC cleric. They will be 8th to 9th lvl when they meet the old couple.

I'm looking for non-lethal effects to basically stop them in their tracks before a blow can be landed or even initiative rolled (technically, this would be considered an "un-winnable" encounter, but the two NPCs are not intended as a combat encounter....).

The idea is that the PCs actions will trigger the effect. That's why I'm leaning towards using "contingency" plus something like mass hold monster or power word stun. Followed by force cage or something similar. They will get a talking to ("If you're willing to be agreeable, we'll free you and you're welcome to some lemonade") and then eventually helped.

But the group has a propensity to attack first and figure out if it was a good idea later and I want to be able to nip that in the bud for this encounter.