It may not be up to you whether you keep him or not, your Cats also have a say and if they vote "no" and show no inclination that they are willing to change their minds then there isn't much you can do about it. Before you do anything else or get too attached, you should take him to your vet to get him tested, vaccinated, and checked out.
Give him a day or so to recover from that then do a slow introduction with your Cats one at a time to see how they react to him, if they're fine then you can think about keeping him but before that you may just be setting yourself up for disappointment.
Give him a day or so to recover from that then do a slow introduction with your Cats one at a time to see how they react to him, if they're fine then you can think about keeping him but before that you may just be setting yourself up for disappointment.