
Hi Karen,
I had one of my pups back for a sleepover (owners were away for a wedding) at 12 weeks and my dogs hardly reacted ;) His mum checked him over to make sure he was one of hers and like you I have a litter sister who was thrilled to see him (read manic

)
I've also had one of the males overnight at almost 11 months and even that went easily - again mum checked him over, he got excited and jumped on her, she showed him a clean set of teeth and he decided to leave her alone :P but the other two enjoyed a new playmate and mum was 100% OK after a couple of hours.
At just 12 weeks I don't think it should be problematic, particularly as you have your own puppy there so he has someone of similar mental and physical abilities to wear down and shouldn't be annoying the older dogs much. I'm sorry his home hasn't worked out - hopefully you will find him a wonderful new forever home and at least you're obviously caring and responsible enough to want to keep in touch and help through any problems. Good luck, Teri
ps. :rolleyes: forgot to say I just walked the pup straight into the house and let the others meet him in the hallway! With the older pup I let them meet in the front garden first :)