Would need pictures to begin to even offer suggestions. But if you are referring to the wall that connects the dormers expect this to be very expensive as you essentially be re-framing a good portion of your roof.

You should be able to remove the intervening wall between the two dormers to create one large dormer and one larger room. Just about anything can be done with enough money. I would consult with a structural engineer or a contractor who has access to and engineer to figure out what will be needed to accomplish your goal.

You can. If you reframe the roof and dormer. Lots of money, but doable.