We took in a stray cat two weeks ago from a family who'd had him living in his garden. He is about 9 months old and hadn't been neutered, but that was sorted when we got him.
He's lovely with us and DS who's 2, but is aggressively attacking our current cat and the neighbourhood cats every time their paths cross. Our current cat fights back when he attacks her, but she's getting quite stressed and pooped under the bed yesterday 
We have 3 litter trays but he just wanders round and pees in all of them so not sure if it's the smell of him or fear he's going to leap out that's stopping her from using them.
They're separated at the moment with own food and litter trays plus feliway diffusers in their main rooms.
Should I just let them get on with it (intervening if it gets too bad) or keep them separated for longer? Aware 2 weeks isn't very long in the grand scheme of things, but really worried he's going to hurt either our current cat or one of the neighbours'.