I would say that in general, yes, people with Aspergers (like myself!) are more loyal to others; friends, family, spouses, bosses, etc...I've certainly felt that way and exhibited the same. In fact, people with disabilities in general tend to be more loyal than the average person; I was told this at one of those warm fuzzy communication seminars I was sent on one time at a former workplace.
My theory though is that loyalty is not a primary "symptom" of having Aspergers; it's more of a secondary/indirect/induced one. Since we realize that we have intrinsically less options than neurotypicals, i.e. we know we can't just "find another good friend (or job) elsewhere", we tend to be more loyal, but this is often detrimental to our needs as humans, because it can mean putting up with abuse, manipulation, pay discrimination, etc, etc. It wasn't till later in my twenties when I really got into self-improvement exercises and I created more options for myself, that I ditched unpleasant relationships with more confidence. Sometimes, loyalty isn't worth it if it doesn't make you feel good/better about yourself.
I know the OP's thread was sort of in relation to family, but I can't speak adequately to that, since I'm lucky not to have any abrasive family members.