Is it normal to be extremely open about sex with your kids

I'm 40 yrs old been married for 20 yrs we have 3 kids together he had 2 kids before me and I had 1 before him we've always been a very sexual couple we've always been very open with our children about sex we've never had sex with the door closed NEVER so when we first got together I caught my daughter and his daughter together sexually I didn't say anything I let them finish then asked them if they knew what they were doing his daughter said yes I just made her feel good I said ok how do you know about that she said my brother and I make each other feel good all the time and that their dad knows and doesn't care she said he taught us how to make each other feel good so that night he and I had sex and I told him what I saw he said its ok baby we will teach our kids not to be ashamed of anything they do and I agreed so now 20 yrs later we all have sex together and our kids love it they say nothing makes them happier I'll do anything to make sure my kids are happy and this makes them happy my oldest daughter and his oldest daughter are madly in love with each other and have been for yrs they have the best relationship but 3 times a month we all get together and have the best sex and I love it my husband is so gentle and loving with our girls its amazing our boys like it rough they are very dominating we are one big happy family