if the property taken is community property or it is not owened by the father of the kid, the kid is liable for the other brothers share of the value.
Actually, if the kid is taking community property with his fathers permission, it is the father, or your brother who can be held liable for the loss to you and your other brother, if you can prove that he gives his son a key and tells him to "take whatever he wants".
He can give away his own property but he cannot give away others. This also applies to damages he causes. He is liable to you and the other brother for your and his share of the value of the damage.
You can't keep him off the property but you can sue him for your 1/3 and the other brother for his 1/3 (presuming this a 3 way deal) losses.
I didn't suggest this in my post, because taking one brother to court over this situation will usually cause more problems between siblings, than it will recover any losses for you.
For example, lets say this 25 year old tells dad that he needs a refrigerator and dad tells him to go take the one at the cabin because no one's using that one much anyway. Then while the kid's there he and his friends break a window or two, dump beer on the TV which ruins it and put cigarette burns in the bearskin rug.
Now you all end up in small claims court. The dad and his kid will claim the windows were broken by vandals and they planned on fixing them next time they go there and the glass only costs ten dollars. The television was an old beat up thing that didn't get any channels clear enough to watch and it probably just died of old age. Even if they admit to taking the refrigerator, what can anyone expect to recover for their 1/3rd share of a used refrigerator? Then dad will also be claiming he repaired the roof and painted the deck which he paid for all the paint and materials for, yada yada yada.
I've seen these situations happen over and over again and there is never any winner, just a bunch of finger pointing, blame passing accusations which ends up making everyone hate each other.
This one uses the cabin five times as much as the other so they should be responsible for five times the wear and tear,,, it just never ends.
Additionally, if the OP expects to win a small claims case against the brother and/or his son, he/she would have to go inspect the cabin, take pictures of everything and do an inventory before and immediately after the son or his dad used it for a weekend and every time they use it.
Otherwise there would be no way to prove that vandals didn't actually do the damages/stealing/borrowing/burning etc.
When a great thing like having a cabin to escape to for the weekend becomes the center of a major family dispute, it certainly takes all the joy out of owning the thing.
So the only solution is to get everyone together and come up with some set of rules that everyone will agree to and adhere to when they use the cabin. Like everyone has to haul their trash away, wash the bed linens, chop firewood for the next guy and not leave a big mess. Basically do all the things that most people would expect of each other if they had any respect for each other.
If you can't get everyone to agree to take care of it for each other, then you need to buy him out, or sell the thing and each of you take your due share.
When you have to use the court system to try to get your brother and his son under control, it just isn't a good idea to have him as a partner.