i'm a firm believer any dog can learn anything (physically possible) if it's shown enough love
what a great person you are for taking the baby in! one thing might be to take him for walks with your babies. that way they learn to interact and that it's "safe" to be around each other. it'll help everyone bond, too, but in a more relaxed environment. bribery will help, as far as his uncertainty with you, also. training is an idea for bonding, too, as long as he isn't scared of you and can be bribed with a reward for doing good. i'm sure once he learns he's safe and has learned that he's well loved he'll pick up potty training in a snap! if he won't come to you, one thing might be to do your routine as normal (like "come on guys, time to potty") but keep the new pupper on a leash. when you say that, just pick up the leash and walk him out, don't make a big ordeal out of it. then do the same for your coming in routine. that way he just learns that it's expected of him, and that it's not a big deal. anywho, good luck and keep us updated!