In normal circs the 1 tray per cat + another tray may be appropriate but when you have 6 cats the idea of 7 trays is a bit daunting. A lot of cats seem to prefer weeing and pooing in different trays and I used to scoop
very regularly before they started going out.
We have 4 trays (none of them small and 1 is a jumbo). We also have a peeing monster but he is aged 9 and been with us 4 years. Amongst the remedies we've tried are Zylkene (supplement that works with some cats to calm them down, I can send you some Susan if you like coz I got in loads for Freddie - seemed to work at 1st but "tailed off"), Feliway, proper thorough clean ups (biological powder and surgical spirit), disinfecting trays with stuff from PAH, urine off (including their completely useless urine detector torch), other enzyme related sprays which I still use .........I've even bought mattress protectors for the beds coz of past duvet peeing ....... Liz on this site calls them "pointers"
She has two such pointers and just cleans up after them which tbh is about where I am now with Freddie but.....
As Oliver is only a kitten, I'm pretty sure he will learn his way out of this behaviour but I would guess it is stress related due to his unhappy early start.
I think I'd go the Feliway/Zylkene route to start with as long as you're quite sure he is OK. Our vets test urine samples for us very cheaply though. Think we get good deals from vet as we are in the 6 cat club
Just saw your last post. I think it's a question of catching them just as they are about to wee elsewhere and quickly pop them into a tray to pee. Easy peasy (not)
I would try and ensure a tray is near to any preferred peeing spot of course.