Have two rescue kittens (and one adult cat), the kitten in question we think is about 13/14 weeks old and the other one is about 11/12 weeks old. They have a litter tray and both use it when generally and definately when shut in at night.
However the older one wee's on soft stuff, I'm not entirely sure if this is weeing or spraying. Not sure how to tell the difference. So far it has been DDs bed, two new cat beds, soft bed bit on cat play centre thingie, any basket of clean washing left out (this is REAL annoying lol).
Any ideas? He's been checked by the vet who found nothing wrong. They are happy kittens and there are no issues with the other cat, he just lets them get on with it.
More likely to be weeing than spraying. You need at least one litter tray per cat, and keep it very very clean as cats are fussy little blighters and will prefer doing it on clean washing than in a slightly used litter tray.
Try this and in the meantime try to keep soft targets (ha ha!) to a minimum.
One of my cats did that when he was about that age but grew out of it. In later life he abandoned the litter tray altogether in favour of the back yard until I moved it to another part of the house then he used it every time.