Run different instances of the proxy for each in separate folders. Same for the miner. Only need 1 instance of the wallet open though. Then on the miners you will need to make sure they use the correct platform. If AMD is your default card then likely the AMD miner would use platform 0 and the nvidia card would be platform 1. If the nvidia card is the main then it would likely be platform 0 and the AMD would be platform 1. You will just have to test to figure out which is which to make it work properly.