Kudos to her for getting out of TWO bad situations. But this is all the more reason not to jump into things with you guys. Agreed with RP. Too much, too fast, mucho NRE. Taking in people with serious life crises going on while in the throes of NRE has not worked well for the majority of posters on this board. Move her into her own place, even if this takes a plan and quite some weeks to put into action. You ALL need the space, even her.
I don't think her child will make matters any easier, since you have said both you and hubby dislike children.
Also, you have been an established tribe for much of your adult lives. I wonder if you ever needed to develop the special brand of "poly communication"? From your back story, it sounds like everything really fell into place with Korre and husband.
I would start reading as though you're new to this. Encourage your family to do the same. Encourage Amber to do the same. If it's going to work, you've got some self work to do too! You've been the centre of your mens' attentions for quite a while. It's natural to feel jealous, but it's going to suck.
Just my random thoughts about the situation. Keep us posted.