You need an experienced electrician.

I'm not even certain that GFCI outlet in the garage is on the same circuit as the bathroom outlets, they are connected to two separate breaker fuses.

If they are on separate breakers then this GFCI has nothing to do with your bathroom. (By the way, breakers are different than fuses. There is no such thing as "breaker fuses".)

Keep searching for a tripped GFCI. That's the most likely situation.

Can you contact the previous owners to see if they know where it is?

Have you tried fully putting the breaker into off position and then turning it on. Sometimes it can be hard to see that it has tripped because it will hardly move. Also, it is possible that the circuits are not labeled correctly. Look to see if one other than one labeled bathroom is off.

The first thing you need to do (after making mainenell's check) is to determine which breaker controls which circuit, both receptacles and lights. If they are labeled, that's a good start, but confirm anyway.