Sorry if it's already been raised by now (I assume we have all been watching super) but why don't we just go as an alternate universe? Then you can make up what ever you want. Their version of humans can even be different, maybe hold some untapped dormant DNA from a mysterious ancient origin. 
Could be a few different powerful races mingled with humans during their own war and only now are humans finding ways to tap into those forgotten powers.

Alternatively it could be a forgotten split timeline (like future trunks universe) but for the parallel universe (6 or 7?).
That way you get all the races you want with a completely altered and varied history and you can still have similar factions, families and even characters.



Best bit, the cannon story is still happening somewhere far away.