my house keep out. Options

[Paws]

Hi everyone, I'm new here. Couldn't see an introductions bit so I'll just jump right in.
My family has 2 cats, and just recently we have been having some random visitors. There is a cat from behind that pops over from time to time, that makes sense, as he lives there. He's only been there about 1 year, so I guess he just got sick of waiting to be invited.
We have a black cat that has started to frequent, and a lovely little ginger. The ginger is surely a female, she's little and pretty and my 2 males don't mind her even when she steals their food of the verandah. She cries under our house but you can't get near her to see if she's okay or has a colar.
The black cat troubles them more, and our posh British Blue has started territorial spraying! He's desexed...isn't that supposed to stop that?