The big question nobody is asking is should they add these characters to the MCU or have a separate universe to build all together.
The MCU is pretty much mapped out for the next 5+ years, building upon a universe that's 11 years old. It will be a challenge to bring in so many earth bound characters that has a long history.
It wouldn't make sense.
The Inhumans would've been easier as their genes are locked so they making it possible for them to be on earth throughout the entire history of the MCU.
If they decide to use build a completely separate universe, they can get real creative in how they introduce characters.
My guess, is they will go the multiverse route with characters ending up on earth with all of them being trapped for good at some point. That makes the most sense.