[Lupin]

I would suggest only one. I regret owning two in a 75 gallons before.:shake:

 

[Lupin]

Can I keep 2 Yellow-Tail Blue Chromis in the same rank??

I have not heard of such species.:squint: I'm confused. First, you mentioned Yellow-Tail Blue Damsel which actually does exist but the latter is not to my knowledge.:roll:

Chromis are a lot better than damsels in terms of aggression level despite the fact that chromis are part of the family of damsels so you might be fine with a 75 gallons provided enough territories are planned out.

It's a long time since I've kept marine fish although I still remember some of them.:lol: But I prefer not to shell out much advice in this other side of the world as it is no longer under my experiences.:lol: