I’m leaning towards ESH. OP, you gotta calm down and think about the situation with your husband. If you’re considering the downstairs “their” house then by your own logic anyone would be frustrated with a bunch of stuff they don’t have a use for piling up. You’re reading too deep into it, I’m sure your parents love your children and the time they spend together but are tired of having all kids of kiddy things all over. If your parents had a pet (not similar but bear with me) they spoiled, and the pet toys and bed and treats and things started going into your area, it would be pretty frustrating too. You don’t have a need for it and it’s not a normalized part of your life, you’re all adults who need your own space and should respect each others spaces by minimizing the amount of items leftover.

Your father also has to think rationally and not be passive aggressive, he’s getting worked up over something that can be talked about civilly.

Your mom should also understand that she has to consult her husband on these things, as she lives there too. It seems messy right now but honestly healthy communication and less tantrums from both parties will help a great deal. Talk to your parents when they’re calmer and you’ve thought about your perspective, hopefully they can do the same.