spongy brakes

My grandfather has and olds 88 that the brakes have became very soft pedal wise. You have to pump up the brake before the pedal feels normal if you just ease on the pedal it will go almost to the floor. No work has been done on the brake system so I wouldnt think air would be a problem. The resevoir is full and there are no leaks in the system. The shoes and pads also have plenty of life on them. Could this be the master cylinder or brake booster? Any way to tell for sure without wasting money?

Also any tips on installing a new cylinder? I will have to bleed the entire brake system correct?

No mention of the year here, but info is available at autozone,.com, repair guides.

Around a 1994 year. Do you think this is the master cylinder?

Assuming no external leaks I would say so, based on your description of the problem.