Holiday with my Sister update

Last year in late July our daughter Karen after our mother was born. She is a very healthy child and the apple of her grandma's eye. Our mother Karen worked out that I'm the father of her new granddaughter, then she confronted Robyn and me about. We confessed that we had sex during our holiday together, Karen said it was okay as little was healthy and she knew we would take good care of her. She then asked were we still having sex together, yes was our reply. Then she asked when were we going to have sex again and I said on the next weekend when Robyn's other 2 were with their father. Karen asked would we mind if she joined in with us for sex, as our father would be away playing golf and he wasn't doing her much now anyway. Our father Donald is 10 years older than Karen and plays golf a lot and it seems he would rather play golf than fuck his wife. Robyn said your most welcome to join us, also that she is going to start trying for another baby soon and that Karen can keep satisfied when she is pregnant again. I just nodded that was 3 weeks ago and Karen is coming over for sex almost every day.