First thoughts: You have several problems. The album covers, the record labels, and the records themselves. There is a turntable/vacuum system that will clean the record and extract dirt from the grooves. These systems work very well. The other two areas involve paper conservation. The first step in that leg is a quantity of desiccant material or blotters to remove the moisture. It’s likely they are beyond redemption but whatever you can salvage or even digitize is useful.
I can’t speak to the value or rarity as I don’t know what albums are under discussion.
I don’t know all of them either, but I’ll be blunt: They’re all covered in mold because they sat in a basement that had flooded, and into which nobody descended into for a good while, leading the records to sit in soaking covers for a couple of weeks. At minimum.
He should have stored them in HIS home and not his parents’, because he doesn’t have a basement. They do.
We told him it was a bad idea, but no...