We have 2 male cats, around 3 years old, and at least one of them is spraying around the house in multiple rooms now and has been doing so for several months or more. Sometimes we see one of them do it, other times we come across it afterwards. They do it on carpet, plastic fabrics, piles of books/papers & other things.
For context- We have cat flaps so both cats are free to go in & out at all times of the day. Both cats have been neutered. They are rescue cats who came together from about 3 months old. They seem to get along most of the time but on occasions do fight. We are a family of 5 with 3 kids so it can be fairly busy.
We've tried most of the standard advice but it's not worked and I've really had enough, so any practical advice would be brilliant.