Empathy for you
I just wanted to reach out to you as the newcomer, as a newcomer is about to join me and my husband, and its very early stages. Our first meetup alltogether will happen this week, excited and nervous. We too have children and our children observe us being affectionate with all our friends and family, so its nothing new to them. We have had a brief tryad in the past and our children did not seem concerned at all when she slept over, and we were affectionate, but not sexually explicit in front of them.
I can totally understand how you would feel, and hope you feel you can discuss this with your partners, and find ways of compromise to work around this issue, i.e, being open around the people you know are more accepting. I know I would struggle being open in front of my family, but I guess we will cross that bridge when we come to it. Having a talk with the children may also be good, depending on their ages. Mine are too young I think to have a formal discussion, but when they are older I hope they will come to understand and respect our choices.
I wish you all the best, and can only encourage honesty in this situation, and seeking those places to go where you will all feel comfortable together.