Depends on how big the Amph and Convicts are. I had a 8" Xiloaenis (similar to Midevil) mercilessly chase down a 3" pair of Cons until he eventually caught them and ate them. IMO, once the Midevil hits a decent size, he/she will likely want to eliminate the pair. If you had a few other medium/large size CA's in the tank, the Midevil would be less drawn to them, therefore the Cons would have a better chance of survival.