Re: 2 circuits
Thats a good question. Be very interested in the answers. You certainly can do that, but I see questiosn on disconnects and bodning. As I read 250.32 exception,if you pull two circuits without a grounding electrode at the barn if they are a multiwire branch circuit.
If we feel 225.30 applies in this situation, it limits you to one branch circuit or feeder.
Putting those two together, I would think, if you used a two=pole OCP and traeted the supply as one multiwire branch circit you would be fine.
There certainly may be other opinions.