33 outlaw, 4 Batteries, 2 switches 10 cables????
 

I don't know how to connect all these batteries! When I got the boat there were 4 empty battery holders 2 switches and a bunch of cables laying under the seat. I figured out the common sense like battery 1 and 2 and the mains.

Do the switches connect to each other? Say I open battery 1 on the port switch, should I have power on starboard engine? And vice versa. I think it should, one cable from switch 1 to switch 2. Or will this cause some madness?
Do the grounds just all loop to each other from one to the next? If not where does the ground from battery 2 go?

It really depends on how you want to hook them up.

You could hook 2 batteries to each switch(#1 and #2) and then connect that switch to one engine.
Downside is if both batteries are dead on one side, you can't combine from the other side

Or you could use 2 isolators.

There are varying ways it can be done.

What do the isolators do? Does that mean some damage can happen if I run a 0awg cable from switch one to switch 2 and the isolator will prevent it?

An isolator is like a one way valve for electricity.
Isolators will connect 2 batteries so both can charge, but will only let the secondary battery drain down with a current draw from it.

It would connect like this

Bat #1--isolator--Bat #2 connected to #1 on Switch #1 and connected to #2 on Switch #2
Bat #3--isolator--Bat #4 connected to #1 on Switch #2 and connected to #2 on switch #1

Personally, I'd do it this way. Simpler and gives more control to you with switches.
I would make both primary starting batteries #1 on each engine/switch.
I would make both secondary batteries #2 on each engine/switch.
I would run deep cycles on #2's and use them as the "house" and stereo batteries.

You would not be able to combine using the switch if one complete side is dead, but you could just use a regular cable in an emergency to essentially jump start yourself.