Those black wires coming into the barn certainly look like 200 amp sized, but then we see these crazy blue wires out in the air with cement in the pipe? whats that?
You dont have to pull the meter. Shut off the service disconnect, mount a panel with a few spaces on a post and board next to the service disconnect and put in 2 100 amp breakers to feed cabin and barn. Then run a neutral to the barn.
I dont see a reason to disturb that 200a service disconnect. do all your changes downstream of it.
the only place that you need the monster wire is the short jump from the existing double lugged disconnect to your new box where you will split into the 2 100 amp services.
The hillbilly "electrician" ran out of pipe and fittings when he got to the barn and just ran it in air thu that big hole? Sad. That area is your biggest danger.