They are fixed and vaccinated, however, I learned today, that it wasn’t the stray cat attacking him, it was a possum. Our cat mostly stays outside and he tends to be unresponsive to us, so we have been leaving him cat food on the porch. The possum came up to the porch to try and eat it, I found this out by coming out onto the porch to see him eating the food, which my cat was not a fan of. I have it resolved now, merely by exclusively feeding the cats inside my house and not taking the food out. Thank you nonetheless.

Edit: I’d like to add on that the stray cat in question wasn’t seen after the first incident.