The main issue I have with RegalHood is if Tamara is RH’s daughter, then Tamara and Neal’s relationship would take on a squicky factor. Tamara was sleeping with Neal, she was going to marry him and then could have potentially given birth to his child.
For me, there’s no more potential squick factor here than with a relationship like CaptainSwan. You get people arguing the whole, “Hook was with Bae’s mother and was therefore Bae’s step-father, so it’s gross if he gets with Emma, who is the mother of Bae’s child.” But that argument doesn’t hold water because Killian and Milah were never married. Sure, they could have potentially had a kid, because they were sleeping together, just like Neal and Tamara could have potentially had a kid. But neither couple did, and neither couple ever formalised their relationship with marriage, so there’s no “keeping it in the family” squick, even if, if you draw a little family tree, they’re not that far apart. Dunno how well this will show up, (turns out it didn’t format properly in the actual post, GAH, just imagine that if someone is a couple’s child, their name is aligned under their parents’ names), but…
Rumple – Milah – Killian
Tamara – Bae – Emma
…so Killian and Emma totally have branches of the family tree (where non-marriage relationships are included) that run parallel. But that doesn’t mean it’s icky if CS hook up.
If we look at the family tree for the other scenario…
Robin – Marian
Regina – Emma – Bae – Tamara
Henry
Especially if we take into consideration that an essential part of the “Tamara is their daughter” theory is that Robin has never really known her because he lost her when she was either a newborn or still unborn, and that he may never meet her if she dies in NL, and the fact that Bae and Tamara weren’t ever actually married, there’s just not enough of a connection there for me to think that RegalHood would be icky.