You say you have two (2) 30A shore power inputs. Fine. That is common with one circuit providing power to air conditioning
and the other to house power. Regardless, you have two inputs.
There are 1 x 30A to 2 x 30A adapters and 1 x 50A to 2 x 30A adapters available. The "male" side (that goes to the dock) are not interchangeable, so you have to work really hard to mess up (*story below).
If you have a 1 x 30A Y you can draw a total of 30A from the dock (protected by the dockside circuit breaker) regardless of distribution between the circuits on your boat.
If you have a 1 x 50A Y you can draw a total of 50A from the dock (protected by the dockside circuit breaker) with no more than 30A on either circuit on your boat (protected by whatever you have on your boat).
At most West Marine
stores there is a big sign over the shore power section that shows all the different connectors for various voltage and current
ratings. I suggest you go stare at that. <grin>
Story -- about three years ago I sold a boat with delivery
from Occoquan VA to Haverstraw NY as part of the deal. The new owner's wife, trying hard to help, managed to get a 30A shore power cord shoved into a 50A dock power connector. *Boom*. Fortunately I had the shore power breakers on the boat turned off and all the new owner had to do was replace the power cord. The shore-side connector was really melted.
If it doesn't fit, look at it and figure out why. Don't force things.