I have a small existing pool house (built 1988) that has electrical service ran to it from the house distribution panel. Two breaker and two separate sets of wires go to the pool house, 240 single phase power for the pool pump (on one 20 amp breaker) and 120 single phase to provide electric to various outlets, fan, etc. (on 15 amp breaker). The services is buried. I would like to put a subpanel in the pool house to have more local control over the loads. So, if I put a subpanel in the pool house, can I combine (20 amp + 15 amp) the feed on the main bus bar and install breakers? I have never seen this before, but if you combined the hots, neutrals, ground, bare ground, in the subpanel, wouldn't this maintain the same current flow through each lead?
National Electrical Code says that you cannot connect conductors 1 AWG or smaller in parallel (310.10(H)). Since it's not likely that the conductors between your buildings are larger than 1AWG, you cannot do what you want.
What you can do, is install a new larger double pole breaker in the main panel. Then install a new set (4 conductors) of larger conductors between the buildings, to feed a secondary panel in the pool house. Then you can feed your branch circuits from the panel in the pool house.
The size of the breaker in the main panel, and the size of the conductors between the buildings will depend on what size service you want to supply to the pool house.