I finally got the courage to invite my brother to one of our sex parties, I've talked to my husband and he didn't mind but the decision was mine and I should do the invitation. I was a bit scared, I didn't know how he reacted, but I got the courage to ask him and he didn't even was surprised. I found out later my husband already told him about our parties he was only waiting for me to invite him. This made things a lot easier after.