I'm going to attempt to tackle your post in its entirety, so bare with any thing I leave out.
Paragon template is unavailable. Factotum might be useful for its action economy, but I doubt I'll have room for it as there are so many other things that could be more helpful.
For the second character, I fully agree that casting trumps melee, but I'm concerned for the lack of a viable meat shield in the party. Maybe a gish? I'd say sharn is out, mainly because I dont want the DM to use them against me, and we have a sort of gentleman's agreement that neither of us will ever do something without expecting the same in return. It helps keep things fun but sane.
As for my power level, I'd like the party to comfortable handle encounters CR 14 from the onset, and be capable of handling up to CR 15 without permanent deaths. This all at character level 12. Most of the encounters will only be right around CR 11-13, but I'd like the extra security.
Prestige classes are allowed on both sides of the build at the same time, as long as the follow a definitive character concept which should be a problem. Dual progression prcs are highly frowned upon.
2 flaws, devotion to an elder evil is allowed, but you cannot change the vile feats it gives(but the list grows from just the vile feats in EE to any vile feat pending DM approval, although obvious traits of evil may lead to pitchfork wielding mobs
).
Character 1:
Eldritch master looks great and will add a great deal of versatility.
If I can squeeze in a way to provide the followers needed, circle magic looks fun, but I have a nagging feeling the followers will just be fodder. It very well may not be the case, but I'd prefer not to risk it.
Incantrix is promising, especially is I can wiggle my way into cheep, or better yet free, persists.
Dwoemerkeeper would probably end up being more work than it's worth as the DM rarely if ever targets my spells will dispells or anything of the ilk.
As for action economy, I'm interested in how metamagic would work. I've used factotum for it, and it requires more feats than I'll probably be able to spare to keep it up for any length of time in any single encounter.
What does Initiate of mystra add to the build? and where is it from again? I've seen it used as a way to combat antimagic fields, but I've never really looked into it, nor used it.
Reserves of Strength is a definite if I boost my CLs by more than just a level or three, too much to be gained to not take it otherwise.
I agree about uncanny foresight, but probably won't have room for spell mastery.
Craft Contingent Spell may be useful, but magic items could be easily ordered through in campaign contacts in all of my DM's previous ones, and I expect the same to hold true. I don't craft wondrous item will be necessary.
Leadership and the ilk are out as we are not supposed to add more characters to the party. The only one allowed would probably be thing like wild cohort/obtain familiar as they are already class features for some. And before thrallherd is mentioned, I don't want to give myself or the DM that headache.
If room is available, Faerie mysteries initiate would be perfect for her. I'm just concerned of the feat crunch gestalt puts on characters.
I think that covers everything. If not, just point out what I missed.