You cannot keep corns with any species of lizard. You can keep them with other corns - and some people recommend against even that. It is clearly possible to keep them with rat snakes as there are hybrids, and they are very closely related.
Any snake considerabley larger than a corn snake may eat it. Anything smaller, may get eaten. It is extremely unwise to put hatchlings in with adults so if you are getting more corns try and get them a similar size as your existing ones, or you will need to keep a hatchling seperate until it's grown on.
Please reconsider introducing any other species other than corn snakes.
Please think very carefully about the welfare of the snakes, everyone wants to see a nice active community tank with loads of different stuff but it can amount to selfishness at the cost of quality of life - or even life full stop, for the animals.
Consider
a) Almost all reptiles have some degrees of cannibalistic tendancies. They are opportunists, and most snakes will eat a lizard in the wild if hungry, or even a smaller snake.
b) Some species of snake such as king snakes are cannibalistic to the point where they will quite happily munch their own species if they can fit it into their mouths.
c) Different species come from different parts of the world. They need different temperatures, humidities, viv sizes, etc. You cannot have a South African Desert creature in with an amazon rainforest creature and provide adequate husbandry for both to survive with high quality of life.
d) Different parasites, mites, etc. live in different species. Cross contamination can lead to problems, high vet bills and sick animals.
I really cannot stress I suppose how important it is that unless you are specific trying to breed a hybrid corn with one of the suitable species, you do not put different species of snake in with each other. Adding any lizard to a snake enclosure is quite frankly, adding livefood. If you specifically wanted to breed a hybrid you would introduce the 2 species purely for mating, ideally in a breeding enclosure, not in either of their vivs, and seperate them after the job is done.
Please.. don't take my word on it, ask other people, read caresheets, talk to your local reptile shop, assuming it's reputable and knowledgeable, and then don't risk it if you care about the animals you have.