So I'll try to make it right without weeks or months of renders, trust me
We do trust you, but I don't think anyone would mind weeks and months of renders of Isa dominating Alex.
More seriously, I don't see them having an actual Dom/sub relationship but, as others have said, I absolutely see Isa as more dominant and Alex as a rebellious sub. I think Alex wouldn't mind someone (or someones) being a bit bossy with her, as long as it's someone she truly trusts and loves. She has her daddy issues after all
She will always push back though, fight a little, but in the end be content and happy with someone protecting and taking care of her. Feeling safe, I think is something she hasn't felt since before her dad died.
I'm less sure about Isa. She has more confidence in her self, and while she has a temper and probably a competitive streak, I think she'll be happiest in a more equal relationship, and she sees Alex as an equal (which is probably something Alex will always find strange, and not quite believe - because supemodel, boobs). Still, for sex-play with Alex, she'll happily play a dominant part. And will enjoy spanking Alex's cute little butt while Frank stuffs her mouth full, almost as much as Joshy will watching them do it.
Nuff rambling thoughts.