they do but they are also very protective
Probably not, as they may try to eat them, and could injure them.
If both dogs are well-trained, de-sexed, and have nothing to fight about, there's no reason why they should not get along.
Well nothing really, I think the fur color or fur feel is different
Ummm.... what do you mean when you say Maltese shihtzu? There's no such thing as a purebred Maltese-shihtzu only a MALTESE and a shihtzu is a shihtzu. If they are mixed then that's the "difference"...