For the last 3 years we've been having 3 sones with my brother and sister in law. We've done every combination you can think of without my husband and his sister bringing involved at the same time. Now they are discussing adding another couple to the mix for variety. But I'm very concerned that it could ruin a good thing! But my husband wants to experience 2 women at once and his sister wants to experience 2 men at once. Fingers crossed that adding another couple to the mix works out!