They have two children, both of whom have been in the show and left, and I very much doubt either of them will be back this time, which is a shame at least for their son (the less said about the actress who played the daughter the better....)
Charlene's step-father will be back, and I assume they will overlap.
Scott's brother is currently in the show, and Charlene's best friend/bridesmaid, and a couple of others they would have known. There's some other family members but no-one they will have interacted with.
TBH I think the 'I wouldn't return without Kylie' line is a neat way to side-step saying 'No, I don't want to go back' without looking like a dick, since we all know that if the show wasn't ending there is no way she'd be making an appearance.