goldfish dont belong in tropical tanks, especially not with the fish you stated
How big is the tank? that red tail cat is gonna need a massive tank when he grows and will probably try to eat the goldfish, depending how big it is, but im not totaly sure as to what red tail cats will eat? but i think they will go after smaller slower fish.
You need to find a home for this goldfish, a coldwater tank of at least 20 gallons, then you can get him a friend.