Male cat having litter box issues
So my parents males famle point siamese in the past year has started going outside the box, usually right outside the box. He is about 5 years old and my parents have taken him to the vet multipul times to make sure nothing is wrong physically. He never used to do this. He now has is own seperate box from the other cat and with this expensive "attracting" litter. He will be good and use it for a few weeks and then he will mark out side again.
Also in the past week or so they have discovered our female cat has peed a couple of times in the kitchen sink. They have no idea why she has done this, as she has never had issues going in the litter box.
Does anyone know why two 5 year old kitties are having issues going outside their box. It isn't health related they know and they have tried so much already but it is stressful for my parents not knowing what is wrong and what will fix it.