Can you use an altered version of a family crest as a logo? Does anyone own the rights to a family crest?

Crests would be protected under copyright law. At this point, in 2012, anything created before 1923 is no longer copyright protected so if the crest was created before then then it is in the public domain and available for everyone's use without permission. However, make sure that you are not using someone else's altered version, because they may have a copyright on their alterations.