No one can say for certain and anyone who pretends to know is fooling themselves. Despite what breed of dog it is adding another dog to the pack is a crap shoot. The three of them may get along or even enjoy each others company. Or, they may not get along and fight with each other. Most adult dogs will tolerate any puppy and appear to get along but when that puppy reaches a certain age then things can happen.
If you are going to add another dog my best advice is to watch them like a hawk and learn each one of their body languages. The trick is to separate them before anything can happen and it can happen fast. Keep break sticks on hand and learn how to use them. also, be prepared to crate and rotate if need be.
Like I said, one never knows but it can certainly be done if you know how to do it. Let's be optimistic and hope everything works out and they become best buds.
BTW, welcome to the forum Julieadams!