Would you be ok if they had more vanilla sex? If not, reconsider your stance because people have sex, pretty much everywhere they can. Of so, also reconsider your stance, because it's up to them how they have sex exactly and as long as they both consent it's all good - they are both happy. And what they do is not your business. Ofc it's okay to not to want to know, but then again shit happens and you won't get to choose everything

Question. exactly HOW often do you just happen to walk into their room without knocking and waiting for the ok to enter? Because if you kept doing that bs to me, I'd tie your son down and peg him just to teach you to bloody knock like a civilised person. Doesn't matter if it's your spare room or not, your raging lack of basic manners or respect for other peoples privacy is the problem here. You wouldn't have seen a damn thing if you had actually knocked and waited or came back later if they asked you to. Stop blaming them and take a long, hard look at yourself in the mirror.

Make them wash the bedding themselves.