To be someone who has engaged in acts of incest

When two relatives have kids. For example, when Oedipus and his mom got down their kids were incested.

Having sex with members of ones own family.

committing incest on a regular basis.

When two family members have sex. I'm not saying that they have to be in/from Albama but hey, almost always are.

A blood relative with enough beauty to warrant serious contemplation of sexual relations.