Would it be bad for a pup to stay with its mother and one sibling until 12 weeks of age? It's a border collie, and we are trying to work around holiday arrangements.

I have one of my pups still here with mum, she is nearly 10 weeks old and not going for another 2.1/2 weeks, she's not with mum full time, just when they have a play in the garden. The only thing I worry about is it might be a bit more stressful to the pup once she leaves here and has to spend her first nights on her own :-(

As long as the breeder is prepared to socialise the pup etc, it shouldn't be a problem. good luck with your little one, we have a Border Collie pup and she is gorgeous ;-) !
Bridget