Car won't move after being parked for a year on incline

It’s unusual to find a paved road much steeper than a 33% grade. Filbert street in San Francisco is about 31% I think, and is one of the steepest in the SF Bay Area. 100% grade is 45 degrees, so 33% is about what you got, 15 degrees. That’s very steep to be jacking up a car, so be extremely cautious. One idea for added safety, park another car up higher on the hill than yours, and tie a cable between them.

In neutral that should be ok as far as the drive train. But it could damage the brakes or possibly the suspension. You need to have a method to prevent your car from crashing into the truck also, should it suddenly come in-stuck. For example the idea above, parking another car further up the hill with a cable to hold yours. This, presuming the pulling truck is below your car.

IMO, overall you’d be better off to follow the advice above, hire a flat bed tow truck to remove it from the spot it is located, either to a shop, or at least a flat spot where you can work on freeing up the rusted brakes.

Any chance you can do something to make it easier for the locked up wheels to slide? I guess you could put a lot of pressure in the tires to decrease the contact patch, and maybe pour water from the uphill side under and below the tires. If it’s cold enough to freeze where you are you could pour water around the tire contact point during a sub-freezing time so ice forms. Time to get creative.