Did you talk to them before getting the car? So did everyone agree where the extra car was going to go. If you’re not going to be allowed in the garage even when it’s clear then it sounds like a conversation might have been missed. The clutter needs to go but if you’ve got an extra car in the household unexpectedly then they can’t be expected to change their lives for it unless they’ve agreed to. They could however be more considerate. Hopefully once it’s clear they’ll see some sense and park one car in there.

For decluttering I’ve got into ‘sort your life out’ on BBC in the UK. They go with the method of sorting things into categories so you can see what you’ve got. That could be a good strategy if your parents have 5 tents and multiples of everything in there. I’ve sorted some of my things that way, and I could tell you I needed every mixing bowl in the house until they were lined up next to each other and I realised how ridiculous it was. I’ve also liked get organised with the home edit on Netflix, thats not decluttering but I’ve got some extended family who have watched it and realised how nice their house could look with less stuff, so it could be a more gentle nudge if you watch it with your mother or whoever might enjoy that kind of show.

Other than that you just need to get started and then they’ll join in. You want it clear so you have to take the lead (with permission). You could start by decluttering your own stuff, if they see how much better that looks then it could inspire them to do the same.

Once you get to the garage, sort everything into categories of stuff, get rid of anything obviously broken as you go, and then ask your parents to sort through a category at a time. Once some stuff is gone you might find that just organising it a bit better will make a lot of room.

It’s also worth looking at if they need help sorting the rest of the house. The garage is often the overflow for clutter.