Any addvice on same litter bitches fighting 12 months old Yorshire terriers
JB

Separate them.

Agree, and if you can't keep them apart one will need to be homed with someone else.  this si oe reason most expereinced breeders and owners advise agains having two of the smae or close in age.

It doesnt just happen with litter sisters.  I can name numerous people who have dogs they have to keep their bitches apart due to not getting on neither is it just confined to bitches it can also happen with bitches and dogs although in my opinion a lot less.