I'm no expert, we've had dogs all our lives and introduced new pups 4 or 5 times over those years. So I'll let you know what worked for us, but must say this pup hubby and son bought me this Christmas is the first pup I've introduced to a YORKIE (10 month old Caleb). ..and Yorkies are different than the big dogs we've always had. More easily offended, hurt, or vocal about how they feel etc.
I'd move the ex pen as you stated it's where your dogs pee pad were. Your dogs lives (and yours for a short while) have been turned upside down. So don't change too many things in their life, that don't need to be changed.
Keep their pee pads, where they've always been.
Pet them first.
Feed them first.
Greet them first.
Give them extra attention, and time without her.
If they will let you, in time hold her on your lap, and them at the same time, giving them their own space as you do so.
Your sister in law needs to be talked with, she may do this again to you or someone else. I'd worry about this pups background. (my family talked with me first, and our new pup is from the same breeder of Caleb, whom I trust) Boy what a situation you've been put in. Is this your brothers wife? Can you talk to him about it, so that no one else is put in this situation.
Any pic's of the pup? Hope he soon fits in and the others grow to love him.......is it a him? A female might be accepted better.
__________________ Caleb   Pippi |