While those (Yorkie?) aren't on my list of "favorite manly dogs to own", I have to respect the fact that you guys rescued the little hairball from a less-than-pleasant existence. I'll echo the above comments...give the dog time. He/She/It has just come from a rather stressful situation, just give it time, don't make any sudden moves or loud noises if possible, and bribes (my dogs go nuts for Beggin Strips, and you can't fail if a bribe is liberally smeared with peanut butter) never hurt anything. The dog will eventually warm up to the rest of the family, but don't be surprised if your relationship just stays at "warm" while all lovey-dovey slobbery kisses and affection are poured out on your Mom. Some dogs just tend to latch on to one human to call their own.
And take that hairball for a walk (the more public the place, the better)! CHI-I-I-I-I-I-CK MAGNET!!!! Dog gets out and about, you (potentially) get phone numbers....its a win-win!