Annoying old cat

[Singlenotsingle]

We have two dcats and a ddog. One cat and the dog are both about 4 years old and don't cause any problems (well, not really!) The other Dcat is 17 and has developed some really strange behaviour. He's suddenly started yowling loudly for no reason at all, especially at night. (the cats are allowed indoors at night but with access outside through a cat flap). He's never done this before.

He's also decided he totally adores my dp, and likes to sit in his lap all the time, which is inconvenient if dp is reading the newspaper or using his Ipad, or eating! If he won't let dcat sit on his lap, dcat sits on the arm of the chair, patting dp on the arm or the shoulder with his paw. If dp is out at work, dcat1 likes to sit on the sofa where I always sit. If I'm there already he slides in behind me and gets sat on if I move back and don't realise he's there! We're wondering if old age has crept up on him and he's losing a few marbles. He still has a healthy appetite thougjh.

The family cat is around the same age. He also yowls for no reason at night. However he is extremely deaf and one theory from the vet is that he wakes, can't hear anything and is calling out because he's scared.
The other theory from the vet is that he is beginning to go down with dementia and wakes up not sure where he is although he's clean and has yet to develop any quirky habits.

I had a mother and son pair of cats. Sadly the son died first (at 18), was pts at home and his mother saw his body as per the vet's advice. For about 6mths after, his mother would wander around the house at night yowling. She would sleep on our bed but it was almost as though she was calling for him as they both used to sleep on the bed wrapped around each other. It was tiring, although I did get used to being woken up, but it was very distressing for all of us because she was obviously devastated. Eventually things calmed down with time.