First be okay with the fact the bathroom tiles might need to be replaced. All of them. Replacing them in the bathroom will have the least impact on the rest of the house and whatever comes out in one piece, can be stored for future cracks. Maybe you can find a similar color but a different size, so it won't look too awkward, just an idea.

Taking out a cracked tile is quite easy. Put on some gloves and safety glasses and (carefully) smash the broken tile with a hammer. An old screwdriver or chisel will help you tilt the pieces out. Work from the hole outwards to remove the other tiles.

Removing a good tile is nearly impossible. Assuming it is still glued firmly, I'd say impossible. But, if you want to try anyway, you'll need to mill out the grout and then figure out a way to lift the tile..

Thanks. That's good to know.
We know our bathroom needs to be sorted as there are gaps in the seal around bath too and with 2 young boys think lots of water has been getting down there!
The windowsill next to the bath is wooden too- don't think someone was thinking when they installed that!
Thought we might be able to save some $ if we could keep the tiles on floor, reseal bath once we have investigated water damage.
Change vanity, lights and tiles around bath though.