hey and Welcome.
mating time is usually from late december to january, your cats should be not problem, they can defend themselves very well with their claws.
from your description it is difficult (not to say impossible) to tell if the fox has rabies or any other illness, you can ask "Words" (member here) he has some foxes visiting him in his garden and cured one from rabies/mange. I would not see it as a problem when some foxes would be visiting my garden.
if you like foxes you should remember, that when you tell a Official Veterinarian, Hunter or "Animal Control" of your foxes, the chances are quite high that they will set traps to kill him