I think you're not unreasonable if you've got that suffocating feeling that every time you turn round, there they are; every time you have a plan, they want to do it too. Everyone needs their space.
I suspect you're stuck with the soccer as it's maybe not worth the potential fall out for the sake of 30 minutes a week, though I get why it annoys you. If you need to, cut back on other arrangements with them - "no, let's leave meeting for supper till next Wednesday/whenever, after all we only just saw you at soccer....." - and use that time to do something else with your son or just the four of you.
I would definitely tackle the favouritism of one child over the other, if you think it's there.
Otherwise, limit information you give them - if they didn't know you had a tent, they wouldn't be thinking of getting one, and you wouldn't be worried you'll go camping, get up in the morning - and there they are camped next to you, or that they'll want to come on trips with you.
If they don't know your husband's having a day off, they can't interfere with your plans for it.
The room and clothes etc for your son is odd, but so what, it's their money and just because it's there, doesn't mean you're obliged to let him stay over if you don't want to.
Pick your battles, and soccer may not be the one to fight - I've also had 2 kids in soccer same time, different fields, and another driver or supervising adult you can drop off while you go to the other game is a wonderful thing, as others say.