OK, so I'm going to marry a u.s citizen and I have overstayed so I'm going to adjust my status. As well as my son's.

But he is almost 18, he will be 18 in July, and we will probably marry in may or June, is it going to be too late for him to adjust?

And do I need to have a valid passport for the interview? And does my son have to go to the interview with us?

First of all, get yourself and your son new passports. You need to submit a copy of your passport with the application.

There will be a problem with your son... since you overstayed your visa, it's recommended to have immigration attorney take care of this matter.