Need help with brake problem

Bad master cylinder or rubber hydraulic hoses are expanding under pressure and needs replacing

I'd go with the other fellow about the master cylinder, though it's conceivable you have an air bubble trapped somewhere and just haven't found it, conceivably in a wheel cylinder. That's going to be difficult to find.

One thing you might try is one of the bleeders that sucks fluid from the bleeder valve, rather than relies on your pumping the brake pedal. It might suck the bubble out.

I'm less confident of the swelling brake line, since they usually have wire mesh and there just isn't much place for a spot to swell. I regret to say I can't guarantee it can't happen.

Good luck and let us know how it comes out.