I've enjoyed having two. Just stick to a schedule when training. Maybe wait til your first is fully potty trained as the new puppy will learn so much from the older one. Will your sister have another litter to pick from?
It bothers me that the mom rejected them. I'm not sure if the pups will have learned whatthey need to from her. I'm sure your sister is a great breeder, but you'll want the best possible puppy available.
Good luck with your decision
