How do go from a single light/fan bathroom switch to a double paddle with no ground or hot wire?
You need to add a three wire out to fan.  Then the black screw gets line in from the panel,the other wire is load out to ,fan light. And only works both together.  3 wire lets them be separate .  White is neutral, on the other screws, black to light red to fan. Need 3 wire to do this. Or leave in a single switch and both run like they did before.