My best suggestion is to work closer with your SCH. As a SCH I will let the WHM know when I can solo heal to let him save MP, he just keeps Regen up in that time. There are lots of times when a WHM can sit back and let the SCH go ham and regen MP, just have to work it out with him as SCH can almost always stay close to max MP.

As for turn specific stuff...

T1, let your SCH handle heavy healing till the split, at that point your MP should last long enough
T2, our group personally has the WHM heal the aoe dmg, but he heals it with Cure/Regen, not Medica, and I focus on whichever tank is tanking. This usually goes until 25% or close to it, at this point WHM starts big aoes/cure 2 and MP shouldn't be an issue before the fight is over.
T4, this one is mostly communicating with each other to let the WHM know when he can take downtime. Especially at the end when it is just the one dreadnought before the AoE starts.
T5, same as above.