The Premise

Here it is:

Ann and Annabelle get married. Wanting children, each carries and delivers an abandoned embryo from a fertility clinic. Thus, Ann and Annabelle begat Jon and Jonathan, respectively.

Then, A&A break up and marry Ed and Edward, respectively. Ann and Ed beget Ron; Annabelle and Edward beget Ronald. A&E and A&E share custody of J&J.

Then, the two A&E's break up. Ed and Edward are out of the picture, replaced by Ken and Kenneth. Respectively.

Then, Ann and Annabelle die in a fiery glider crash, leaving Ken and Kenneth with Jon, Ron, Jonathan, and Ronald.

In the aftermath of the deaths of A&A, K&K find love together and marry. Together, they have joint custody of their various step-sons.

I call it, The Aristocrats.
Or possibly, One Step at a Time.

Also, all their grandfathers are vampires.