alright for those confused about the threesome scene, here's how i got mine:
got diane pregnant, waited a few weeks (go to bed, wake up, go to bed etc etc) eventually she starts getting a belly bump, continue the wait until she gives birth at the hospital, wait 2 days and check the hospital, if she's not there, you'll see her with the baby in your house at night (not midnight). she'll continue looking after the baby (you'll see her holding her at night in your house and in the barn during the day) for two weeks so keep going through days until the baby is no longer with her. then at night (not midnight) go to see mum, diane will stop you and the rest you just gotta watch for yourself because i don't wanna spoil it.
i hope this helps.
edit: i forgot to mention. the threesome scene is repeatable. after the first time, you'll find mum and diane waiting for you in mum's bed at night (not midnight). if you go to her room at midnight you'll have the old scenes with mum only.
edit 2: and also my save