I think it might be hard to find a word that relates exclusively to the family, outside of rather technical terms. With that in mind, I'd maybe try applying more general purpose words, and put them into context with the rest of the sentence. For example, you could use words like insular or detached.
Insular is an adjective that means: remote, detached, or aloof; isolated or separated.
Wiktionary defines insular as: Having an inward-looking, standoffish, or withdrawn manner.
Detached is defined as: not feeling involved with someone or something in a close or emotional way.
Again, these are not words that completely convey what you want, not as a single word. When insular is used to describe a person, it usually refers to someone who is a loner in general, not just toward family members. Detached can mean someone is withdrawn, and might imply a vacant sullenness. However, one might still use these words to apply to a family member who would prefer to stay with friends, and avoid the rest of the clan:
My brother is very insular toward his family.
My brother stays rather detached from the family.