Before you do anything else, clean the terminals and cable connectors on ALL of your batteries, and ensure that your batteries are actually good (test them) or you will be chasing electrical issues that may simply be battery problems.
Do the heads (toilets) have foot pedals on them? If they do, they work on vacuum and each head will have a vacuum generator somewhere between the head and the holding tank as noted in the diagram of the first link of my post above. Depending on the model, there will be a pump there that looks similar to this
http://yachtvolare.blogspot.ca/2013/03/fixing-vacuflush.htmlI've seen these in engine compartments, under stairs, under beds, under benches, behind wall panels, in closets, behind fridges, etc. Wherever the boat manufacturer figures it will be the most difficult to get at

Your first task should be to check and see if you are getting 12 volts to the pump. There will be a breaker at the electrical panel, and they will sometimes have an in-line fuse at the pump. A bad vacuum switch seen here will also prevent the unit prom running. The assembly should have a square coveer on it.
http://www.environmentalmarine.com/kit-vacuum-switch-vgii-310540/These systems typically run off your fresh water system so it needs to be working as well. When the pedal is partially depressed, it will allow water into the bowl. When it's pushed all the way, the ball in the bowl will open and the vacuum will take everything away. When you finally get the system running, remember that the water in the bowl helps to make a proper vacuum seal, so again, the water system must be working or you can pour water in the bowl for testing purposes.
The 3rd picture in your last post is a macerator (by the battery) for overboard discharge.
If the vessel was partially submerged, ANY wiring, connectors, electrical hardware, etc. that was under water is suspect as a possible cause for its respective system not working. Unfortunately, it's likely that you will continue to have gremlins and system failures until all the electrical hardware is cleaned up or replaced.
PS: if you can't get the on-board water system working just yet, why not hook up your dock-side water? There should be a fitting in the cockpit where you can hook up a potable hose from the dock to the boat. This will give you pressurized water and allow you to take a shower providing the water heater works.
***PPS: I just saw the vacuum genrator in your 3rd picture behind the macerator! it is the while plastic tank. the vacuum pump should be mounted on it or beside it.