I am not familiar with your motorhome model but I would hazard a guess that the twin batteries will be your leisure batteries because vehicle makers are never very fond of giving two of anything when one will do
seriously though can you see the batteries easily if so the engine battery will have heavy starter cables clamped to the terminals so check the single battery first, the leisure batteries often have multiple wires coming from the positive and negative. HOWEVER your M/H is quite modern and it may have been wired up with a fuse board in a cupboard for instance and all the circuits distributed from there.
If that is the case you can check with a multimeter by disconnecting the positive terminal on say the 2x batteries and if you lose power at the fuseboard those are the leisure batteries. or even simpler do as said above and try switching a light on that will prove whether you have identified the right batteries.
As you have a solar panel I would go with the 2x batteries being your leirsure batteries.
I hope that helps.
regards Phil