Ive been wondering this for some time now. If you were to make an Avengers team, With the U Wasp and her defense of nineteen, could you use Thunderbolts to copy Fantastic Four AND use their alternate team ability to make everyones defense 19? Also, would Cap's energy shield/deflection make his defense 21?

No. From the Marvel FAQ:

Characters assigned the Thunderbolts feat may not choose a team ability that is granted by a feat card when choosing a team ability.

You can choose the FF TA with Thunderbolts, but it will always be the original TA. You can choose to copy the Defenders/JSA TA, and share Wasp's DV that way. And, yes, if you could share Wasp's DV with Cap, his DV with ES/D would be a 21.

The best thing you could do here is make the Avengers the Defenders or JSA. And Ant-man is a better choice than Wasp, though Wasp can Taxi...