1) two young pups will likely bond very closely with each other rather than to the people that own them which is hard to avoid, and can cause behaviour problems as they grow -- and the owners will need to put in a LOT of time with each pup separately to train and so on. Two pups is as hard as twin babies -- everything has to be done twice and unique to each pup andf one pup alone is a serious amount of work and time. Also siblings do not always get along very well as they get older. I know many people who have successfully brought up two puppies together but a good breeder will advise carefully on doing this and it is wise to realise from the start how much work this is going to be. Many good breeders will not home two pups at the same time or two pups from the same litter for these reasons. I don't mean to overly worrry anyone but these are very real worries and extra work will be required as well as a very vigilant eye to prevent problems from the start. Not least because two puppies are so cute playing together than the temtpation can be to just let them spend all their time together and let them get away with whatever they want as it is charming. But what is charming at 4 months is not so charming as 12 months and may need a lot of remedial work. So just be aware, anyone thinking about two pups together.