I had 2 Oriental Lilac cats (mother and daughter) that this happened to. When I took them to the vet, it turned out they both had tumours on their lungs which turned out to be cancer.
Do you provide them with any toys - and - do you yourself actually play with them? Do you fuss over them and give them any incentive at all not to wreck you home? I think they're just being lively young cats. It's perfectly normal. We used to have a Burmese who used to wreck if she was board...
Perhaps the litter you're using isn't to his liking. I'd look into changing it to a different type if that were me. If not, please seek advice from a vet as there may be something wrong.
It's not good to leave a cat alone all day without a companion. We have 2 British Shorthairs (brother and sister). I amout of the house from 6.15am until 5.45pm. However my husband comes home lunch time for an hour every day. So, that's not too bad.
The Association of breeders of Siamese might be interested in this (or not). Also, the GCCF (Governing Council of the Cat Fancy) should be informed. This isn't the sort of thing that should happen. Reputable pedigree kitten breeders have their litters at home and, any prospective purchaser goes...
Smokie (our Blue Burmese, who sadly is no longer with us now) attacked my father in law when they visited us at our new house years ago. In all fairness, Smokie had never seen them before. He was just like a tiger the way he sprang. No, we didn't have him put down at all. Never even thought of...
It's wrong to keep a kitten isolated like this. That is possibly why he's wrecking things. Cant you integrate him with your other cats - they'll get used to him eventually?
Not having a dig at you - honest. It annoys me though when people get cats for one reason or another, then get angry when...