When do you think Peter will tell Olivia about Henry?

i hope never. there's no reason to. all it would do is dredge up bad memories from their past. Though, the fact that they call her the female version of Henry, does tend to indicate that Peter does tell her at some point. Then again, it's quite possible that Olivia could remember the cab driver on her own and remember what he did for her and decide to call the baby the female version of his name. But if i had to pick a point in time when he told her, i guess i would go with after they had Etta. Then maybe she wouldn't be hurt as much por Peter having a child with the fake her.

No, never. You don't tell your girlfriend about the kid you (sort of) had with the other version of her
No.

Henry was erased from time por the observers so none of that happened to alt Olivia or our peter but peter was told about henry when he returned as the observer wanted to explained why he was back