Someone asked about the logistics of sharing space.
On the one hand, finding space for private time with a partner is all about logistics*. On the other hand, it's also an emotional issue to deal with, especially if you live with one (or more) of your partners.
If you live with a partner and share a bedroom, do you have sex with other people in that bed? Some couples do that only if both of them are there and playing with a third person, and otherwise use a guest room. Some couples don't mind at all if one partner has sex with someone else in the bed, as long as sie is not left waiting to go to sleep on a work night!
Personally, unless I like my partner's other partner a lot, chances are good that I want my partner to change the sheets on hir bed between partners. That can be a lot of bother if you're doing something like every other night, though!
And, of course, there are questions about noise*. How do you feel about hearing your partner having sex with someone else? Does it turn you on, or make you feel warm and fuzzy, or does it grate like nails on a chalkboard? How do you deal with that?
Communicate, communicate, communicate, of course, and be as gentle and respectful of your partners' needs as you wish they were of yours. Remember that just because something bothers you doesn't mean it will bother your partner or occur to hir that it will bother you. Remember that there are things that are going to bother your partner that don't bother you!
* Dealing with sharing space with kids, of course, complicate things even more - but that's another post.