Is it allowed to keep kitten or cats as a pet in one’s house.Are their excretion najisTheir urine and stools are najis?What are the rules regarding making oneself and the floor/place paak if touched by their excretions?

Cats are permissible to have, but it is not allowed to pray with cat hair on ones clothes. This is because, even though being Tahir, we are not allowed to pray with fur from an animal that is forbidden to eat.

Yes their urine and excretion is najas

To clean urine you must was with water twice when using leas than Kurr water or either once with Kurr water or something connected to kurr water

Excretion needs to be cleaned with water once.