You're talking about a couple of different things. Your toilet leak is probably traveling through the floor and dripping onto the top of the kitchen drywall. Same with any leaks coming from the shower, whether from over spilled water, or from water leaking around the drain.
You also mention leaking pipes. If they're leaking it's either inside the ceiling or one of the upstairs walls. Unfortunately, you won't know which until you start to remove drywall and look for a leaky pipe. I'd start with the kitchen ceiling because of the mold possibility mentioned above. If you find a wet pipe, but also find that the water is running down a vertical pipe, then you'll have to open up the 2nd floor wall too.