It could be allergies...cats are very prone to sinus issues...so hopefully that is all it is as everything is starting to bloom.

It is hard to sort out back-porch feeders. Could you put the food for him in a separate area? It sounds as if the girls have accepted him as part of their group. As an unneutered tom he will probably spend much of his time wandering looking for "love" and only returning for rest and food. In my experience with cats, a young tom is unlikely to bother an older female whether she is spayed or not. He might try to mate her, but in cay colonies it is usually the elder female who is respected. (Like anything, there are exceptions)

Good luck... and thank you for having time and compassion for the poor needy ones.