I have been thinking about this issue and for the time being I call Bullshit.

I don't believe Desi and Elli are blood-related, they only share the same last name. They portray themselves as mother/daughter. This has a distinct marketing advantage.

There are a lot of people that have the same last name, who are not related. Teagan Presley isn't family with Elvis. Byron Long is not Donkey's brother. Etc.

So, until I'm showed certified DNA tests, they're just two more whores doing a B/G/G scene. And not even a real one, as the stuntcock took some time off between fucking them to take a shower (which is saying something, I think).