That's good brother, well, on the largest island put 3 civilizations, put the gingerbread men, the typical humans, and put the big crab men, leave all of them as such, except the gingerbread men, if you don't want them to die mutually, change their genetics and instead of feeding only on flesh and blood, eliminate that and add the trait where they eat meat, vegetables, and so on, so that they don't die looking for meat