12 isn't actually that old for a cat. You say they're long haired and you're sick of hair, do they get groomed regularly with a comb or brush?

The pooping ouside the box could be solved by getting a box with a cover over it so they can't poop ouside of it, also make sure litter is cleaned out regularly as some cats don't like to go if another cat has 'been' in it. Make sure you get rid of all the traces of the smell of the poop where the cat has left it as it will encourage the cat to go again in the same place. Using bio washing powder and then putting a little vinegar in the rinsing water will get rid of the smell (even if we can't smell it the animals can).

If one of the animals is on medication for a condition then it should still be on it whether you think it's doing them any good or not. The thyroid problems are going to be detrimental to the cats health, as it's running on top speed as it were. They can suffer from weight loss, increase in appetite, hair loss or patchy hair, some cats can have bulky or large amounts of stools. The medication helps to control all this.

I'm sure someone on the forums can help you more than I can, as they may have a cat with the same condition. Many members have long haired cats and can help you with that side of things as well.