Will this fit the 8bitdo ultimate controller for switch?

Yes, it will fit the controller.

Will these store wii u pro controllers comfortably?

As my video demonstrates. It's a tight fit, but it should be okay for the WiiU Pro Controller. If you're worried about the sticks, maybe cut the mesh out so the sticks don't rub against it. Hope this helps!

Will this fit joy cons with the grip attached?

Hey! The good news is that the grips with 2 joycons do fit inside the case! The bad news is that it's rather loose. This wouldn't be an issue if it was just loose side to side, but it's loose top to bottom too, meaning the joycons' joysticks could potentially be damaged in there. Joy cons especially have a joystick problem, so maybe keep the lesser ones in there while preserving the good ones in a regular switch case. Happy travels! (P.S also tried it with the Xbox one controller while I was here. It fits wonderfully, no looseness at all! Might be unrelated but helpful to someone else at least