RV parking

Parking brakes ( the springs that set the brakes ) are on the rear wheels only, never the front brakes they are always free wheeling unless the service brake is pressed! This is why your rear wheels should never leave the ground without blocking the front well. Your stuck front brake is not related to the spring brakes being set ( they should always be set as a side note and to answer your question ) block the coach so it can't roll and hit the brake shoes ( drum brakes) with a hammer ... Very common for brakes to stick rust freeze whatever
if you do use the reverse the tranny method be VERY careful as the torque can easily twist your driveline off. Give it a try first but be very gentle