Typically they put the second AC on the second lead. The hotwater heater, microwave and electric fireplace are most likely an unknown. If you have the PI remote on your surge protector(everyone with 50 service should have one), you can document what is on each leg, buy turning them on one at a time. Your question is prompting me to do that in our unit, and put up a list in our switch cabinet.
Note on 50 amp units. If you loose neutral on 50 amp service you put 240V across all AC items. You burn up the converter, the microwave, TV, AC on and on.
Chris
2021 F150 2.7 Ecoboost - Summer Home 2017 Bighorn 3575el. Can Am Spyder RT-L Chrome, Kawasaki KRX1000. Retired and enjoying it! RIP DW 07-05-2021