A lot of cosplayers have a limit for 90% of the content, I know a WoW cosplayer who will do full nudes but no masturbation content for $200 (I've bought a few), but she doesn't advertise it, I'm sure the twins have the same deal, you have to want to spend alot of money or offer alot and they might, but if you making $1000+ per PPV and someone is offering $100-200 and they wont be able to resell it, you can understand why they don't do it.
And I'm pretty sure, going off a response from Linnea, is she wants to do it, but she's afraid that its not going to be for a limited number of people, that it's going to get leaked, so I'm gonna take a guess, she'll need alot of money for her to do it.