If he’s unaltered, in his condition he won’t last long. The other male cats or bigger critters will get him.
If it were me and I could get him into a carrier I would take him to the vet. Have him tested for the bad diseases first to determine if he should be put down.
Fleas, ticks, worms etc can be taken care of cheaply. The mange is contagious so be sure to wash your hands after touching him. Mange is easy to treat and not very expensive to treat either.
I recently took in a stray kitten with ringworm. It’s been 8 weeks of keeping him separated from my other cats to be sure it’s gone. Baths twice a week, cream twice a day, but it just never seems to go away completely.
The little guy needs help. Good luck.
A sulpher-lime dip will get ride of ringworm fast.
My ex-wife had a friendly feral cat around her yard. She took it to the vets for some treatment, and they gave her the cat back, dead. She felt very, very guilty!