You have my sympathy!
Never, ever in my wildest dreams did I imagine it would be so difficult intergrating a puppy into a "geriatric" home where the youngest is 8 and the oldest is 13.
Owain was 9 1/2 wks when he came home, they all hated him from Day ONE and Nicholas was terrified of him. He tried to chase them, bite them, etc and so it ended that he didn't have anything to do with them. Meanwhile if he did get near them, he hurt them, they ended up at the chiropractor and everyone was miserable. I had thought they would correct his behaviour but they didn't.
For months it was sheer misery and many times I talked to the breeder who is a very good friend, fortunately, about sending him back as he didn't fit in, not for the lack of trying.
Fast forward to January 11th, that being his 7 month old birthday. That day it was like he woke up, decided to grow up, the others decided he was OK and suddently everyone settled down and became great buddies. It was the weirdest thing I have ever seen.
He still has his moments and I wouldn't leave him alone with any of them unsupervised and I don't know if Gracie the 13 yr old trusts him but life has improved so much.
So, hang in there and I hope things work out between them. It is very hard isn't it having a puppy after all those years!!