Replacing rusted light switches
Cleanup time!

The daisy-chaining simply means that instead of using short wire "pigtails" from a terminal screw on each switch to a wire nut that connects all the pigtails to the incoming hot wire, the incoming hot wire was stripped in places which were then wrapped around a terminal screw of each switch in turn.  As long as the contact surfaces of the wire and screws are still good (i.e. not corroded), things are still OK here -- any corrosion on the bared wire surfaces should be removed mechanically with a stiff wire bristle brush (think of it like prepping aluminum wire for termination) in order to preserve the integrity of the connection, however.

As to the switches with the rusted yokes -- I'd simply replace them with decent spec-grade switches, and make sure whatever was allowing water ingress into the box has been fixed as even when its not shocking you, the mix of water and electricity is notable for its destructive power, as you can see here. (More precisely, corrosion is an electrochemical process rather akin to that going on inside your average battery, so an external electric current source has the potential to accelerate the corrosion process.)