Welcome to Librarium Online!
Let's say I have a Vampire Lord and two Vampires with MotBA and I roll double 6 for my Winds of Magic. Now, I know the main power pool cannot exceed 12 for any reason, but since only the Vamp with MotBA can use his extra 2 power dice, could I have a pool of 12 and then three Vamps with two more each?
Nope it states in the errata that Motba Counts towards the PD limit but opnly the vamp with the power can use those two dice so if you roll Double 6 then you lose 6 of them if you have 3x Motba vamps as their power over rides your dice roll better to only take one Motba at most nower days
I actually think taking two is just fine. The number crunching is as followed:
One MotBA: 70.6% of not getting over 10 at least once in five turns.
Two MotBA: 42.1% of not getting over 8 at least once in five turns.
So yes, you have more of a chance to roll over 8 at least once. But out of those times you don't, you have at least 5 dice advantage (ignoring them having more dispell, etc). Now it should be considered that channeling could still go off raising the chances of passing twelve by even more. I would have to assume number of wizards for that.
So one is great. Two might be pushing it. Three is beyond overkill.