Puck was dating Rachel when he got Quinn pregnant with Beth, Rachel leaves Lima but is pregnant by Puck also, She comes back a few years later and Quinn is married to Sam, I think she might be pregnant or recently had Sam's child I'm sure there was an extra baby in there somewhere. Rachel at first doesn't tell Puck that he is the father of her child but he works it out eventually.
I remember a scene in Quinn's kitchen with Brittany and Santana talking about missing Rachel and at some point Santana pulls her up about leaving them too and that they didn't do anything to hurt her so why didn't she keep in touch with them.
I'm not sure if I'm taking this from the right story or not but I think it was in this fic where Puck takes Rachel's daughter to meet his family and Beth introduces her sister to Nana Connie. I think in this fic Puck has more than just his younger sister, there's other siblings in the family and nieces and nephews.
I can't remember if the story was complete or not.
Any help would be hugely appreciated, it's driving me mad trying to find it.