Can you solve these endgame studies?

Yes, these are good finishes! Due to the open positions it will be hard to extend them to more substantial studies. Both sides have so many options that you can't give away the initiative and expect a favorable outcome. Zugzwang is therefore pretty hard to accomplish. There are however many zz positions with other minimal distributions like K+Q vs K+Q+B! These have been explored by Belgian composers.
Btw, your last finish with underpromotion in that topic is very promising . I will post a more elaborate study version later!