As I stand there watching my son finger my daughter my cock began to get harder than I ever thought possible. I couldn't help but reach inside my boxers and start slowly stroking the length inside.I watched Max add a second finger into Sam's dripping wet pussy."Oh Max, fuck that feels so good. Mmmmmmm please don't stop uhhhh mmmmm." "Yeah? you like that sis? Then watch this!"At that Max got up, spread and laid between his...