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Eternal Yoshi
If your opponent's attacking in the air, block high. If they're attacking on the ground, you block low. The exception is overheads, which are ground attacks that must be blocked high, like Akuma's Forward-M.
There's a lot more factors going on in Marvel though (which is why I generally don't recommend people start out with it), but for 2D fighters that's basically what it comes down to.
I don't play Marvel anymore, but I can say your team has a bit of questionable synergy. Tasky's not that great on point. He's not that mobile, his mixup is lacking so it's hard for him to open people up, and his keepaway, while solid, isn't as good some of the better zoners in the game. Also, his assists and DHC's are pretty good, so they kind of go to waste when he sits on point.
Frank is just not worth using unless you plan to sufficiently level him. Shopping Cart assist is great, but Lv 4 or 5 Frank is one of the best characters in the game, so you usually build the team around helping him reach that level, rather than the other way around. Most teams with Frank involve scoring a combo with a lot of hits with a point character (usually Dante), empty DHC'ing to Frank and then taking the snap shot straight to level 4.
Ammy as an anchor is fine. She's fast as hell and strong as hell with X-factor, has a good assist, and will have quite a lot of meter sitting in the back. But I don't see how Frank or Ammy's assists benefit Taskmaster. Again, his mixup is bad, so he can't really take advantage of these lockdown assists.