3-SOME MOVES FOR 2 PEOPLE

While it doesn't give you three people in the animation, you can perform threesome animations with only two people.

Invite your partner to a threesome, and have them accept. Close the information boxes in the upper left of screens. Then press your F5 key to reload the region ( only you, not your partner). Return to your partner and invite them again to a threesome. You will both end up on the bed with the threesome animations available.

Again, it doesn't give you three bodies, but it does unlock the animations for two people which can be fun with a bit of imagination and creativity.