No, there is no charge for Disney resort to DIsney resort, If you are on the Beach Side and they stay on the Yacht side you should be able to just dial the room number and get them directly as they are technically one resort (and the room numbers are not the same). If not just dial 0 from your room phone (that is the "Disney" operator) and ask to be connected to your other party at the Yacht Club, or hit the front desk button on your room phone and ask to be connected to the other party.
As far as room size goes the Studios are about 356 sq ft of space with a Queen bed and a pull out sleeper sofa. They have a microwave, a mini fridge and a wet bar area (Just for reference a Yacht Club standard room is about the same size, just a little smaller but you lose the wet bar, fridge and microwave). Where the 1 bedroom has a living room (pull out sleeper sofa), full kitchen, master bedroom (king bed) and a luxury bath. The 1 bedroom is 762 sq ft.