Our siamese cat, female,7 years old,spayed,declawed,pees where ever our other cat sleeps.she is also quite aggressive and chases her around the house.we have had the siamese for 6 months as the previous owner passed on.the vet checked her and she is fine.our other cat is a 7 year old gentle little persion,any help would be welcome

Lock the siamese cat in a cadge and put the cadge somewhere in a room in your house and let the cat pee in its cadge. It's like giving the cat 'a taste of its on medicine'. When it meows let it out, but if it pees again put it back in the cadge. Do this over and over again until the cat stops.

The first thing that needs to be done is rule out medical issues such as bladder infection or kidney disease.
If a vet check turns up nothing then you may have a cat who is showing her displeasure for her new housemate.
Cats do not like to share their turf as a rule, some will do fine others will not.
I would certainly not lock her in a cage that will only be more upsetting to her.
You will need to clean the areas she has urinated in with a good enzyme cleaner.
And I really hope the new cat doesn't sleep in places like your bed, your sofa, etc.
You may never get the smell out.
Is your house set up so that they could each have their own space and then be gradually reintroduced?
Some cats simply will not accept another cat in the house after they have been queen bee for all those years.
I hope that is not the case.
Start with determining whether it is a medical problem and go from there.
If there is a problem, and it is not detected and treated then you will be essentially beating your head against a wall trying to fix the problem.