Alright, I need to call in back up....
We're starting up D&D at my library, and I volunteered to DM, as our former librarians/DM's moved. I've got the knowledge of the game, and it's a group of my good friends, but I'm forecasted to DM for up to ten players, ranging from completely new to a few veterans (who now how to play, by no means munchkins or power players). So I was planning to split them into two groups, meaning everyone gets a chance to play and I don't have to run a 15 monster encounter every time. So what follows is what I have so far

1:Two kingdoms are at war. Over land,morals, religion etc. But for the most part that's irrelevant. One kingdom, ruled by King Robert and Queen Megan is good aligned. The other kingdom is ruled by the evil wizard Myrn, is of course evil. If I'm dividing into two groups, each will represent the kingdoms warriors, and undergo quests to stop the opposing monarchy. If I have only one group, I'll stick to the good.

2:The separate, but parallel missions will culminate in a clash between the two forces.

So here's what I need help with:
How should I make balanced but distinct teams at lower levels? I'm planing on
starting it at level 3. Mostly core but with supplements sparingly.