My wife was killed by a drunk when our daughter was only two. I couldn't stand being reminded of our loss, so we moved away to make a new life. We made some real good friends in our new home.
An adult brother and sister (with flashbacks to their teen years) and his two teen daughters and their life together, swinging with neighbors, until they come to realize that they are more than just brother and sister. Note there is bisexual male/male sex and some watersports.
Almost 40 years ago, our hero found a small Appalachian town where all the women had recently been blessed with bigger breasts and the men had become sterile. What did our hero do? Starts with minimal sex. That will change as as the story continues. (Tags include action in future updates)