[hobbsmann]

The answers to your first two questions are interrelated and given you have underrepresented your hand by not capping preflop capping the flop is just right IMO. I think it changes if you cap preflop and the action proceeds in a similar fashion then I think calling CO's 3-bet would be best.

As for the turn action I think I like calling with the plan to not overcall on the river UI (in which you have 2 Q outs and probably have the remaining 2s and 4s as outs to counterfeit a two pair hand).

Thinking about it more EP cold calling two means he has a T or worse the majority of time so him calling in between you and UTG1 doesn't mean much. I'm not sure about the river now as given the pot size an overplayed KT/AT is enough of a possibility to warrant a call right?