Not sure about how to get him in, but I wouldn't let him interact with your kitties at all until he's been tested for feline diseases.
How long has he been out there? Does he belong to anyone, that you know of?
I stole Matrix from our neighbors, but from a legal standpoint, he was already ours. AZ state law says that if you keep or feed an animal for six days, the animal belongs to you. (This is how some people get stuck with feral colonies, because this law isn't common knowledge).
Matrix's abandoners (won't even refer to them as previous owners) left him outside while their other two cats lived a cozy indoor life.
They never even put food out for him, so for about a year or so, we fed him.
He was always super friendly. Came up to us and let us pet him and love on him. One day I just looked at him, picked him up, and took him inside. Had him microchipped and tested the next day. Now he's my bubby.
Just check your laws and make sure you're not taking him illegally. Maybe even have him checked for a chip.
The only thing I could think of, since he won't let you pet him, is setting out a humane trap to catch him.
I believe most shelters or humane societies will rent them out.