Can repair work be done from the apartment unit below ours although the source of water leak is from our bathroom ?

Depends on the leak. If you have a leaking drain, the repairs could be made through the ceiling below.

Harold said it: it depends. It can be:

1. leaking overflow / rough
2. leaking trap
3. leaking overflow / trim
4. leaking spout
5. leaking shower arm
6. missing grout
7. overspilll / leaking through floor
8. leaking tub itself / crack
9. leaking valve body
10. Leak around the valve trim

And more...

Experienced plumber will first observe your tub and surroundings before he/she touches anything. In many cases, he knows where the leak is w/o even touching anything...

can repair work be done from the apartment unit below ours although the source of water leak is from our bathroom ?

Before anything can be done both the type of the leak must be determined , (drainage leak or pressure leak?) and the sorce. Only then can you start a repair. So let's have more details. Tom