Getting your own mother pregnant, then getting that daughter/sister pregnant. Therefore, it's a sister within a sister. Inception + Incest = Incestion

INCESTion is the act of fucking your wife while she's pregnant and sticking your penus soooo far in that it goes In your babies mouth. Therefore, you are somewhat being an incest.

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.