Duel fuel gauges, windlass remote

My Carver 355 has the same fuel gauge setup, momentary switch to view levels. It is a bit strange and I would like to change that as well, but is a long way down the todo list. Should be easy enough, install the gauge and readjust the wire from the momentary switch. Just remember to shutoff electrical power to the helm when leaving the boat for extending periods so the gauges don't drain the battery. Very little drainage but drain it will.
I recently had to change both the sending units, the port was a real pain due to access.

I wouldn't bother adding the gauge. They're not all that accurate anyway. Besides, they'll burn pretty close to equal. So, when it starts going down take a second and flip the switch for peace of mind. It'll take you less time to get used to this situation than it will to change the gauges.
As for the windless wire, you can run it above the headliner in the cabin. Install a second switch at the bow. You'll probably use that one more.

The headliner is the soft ceiling which is generally held in place with clips, however, if you have a conduit, does it lead to the engineroom or is the battery in the v-berth? If it runs to the engine room then use that. Run the wires to the engine room and then follow the helm controls up. If not, go above the headliner, then up the post (probably one back from the winshield) that carries the helm controls up from the engine room to the bridge.

Regarding the fuel tanks, are they connected together? Meaning do they use fuel at the same rate from both tanks or do you have to switch back and forth?
If they are used equally, wouldn't it make more sense to run them low and plumb an equalizing tube between them? Then 1 single gauge would read both tanks and you would be able to balance the fuel use without trying.

My Carver 355 diesel saddle tanks are connected together with a transfer pump.
The genset is fed only from the port saddle tank. The transfer pump lines enter the tanks from the top. I would not consider installing a equalizing line between the saddle tanks because that would require putting a hole in the tank below the fuel line. Not a good idea. It would be just a matter of time before a leak would develop.
Gas boats of the same size I believe do not have the transfer pump for reasons I don't know.

One of the best reasons I can think of is gasoline and electric motors in confined spaces are not the best of friends, indeed they may come to have an explosive relationship.

You already hve the lines and valves in place, but it sounds like just a replumbing could handle your problem (if equalizing was an option).

Clamp of the hoses from the saddle tanks, drain the fuel from the hoses, place a 4-way Jandy-type valve:
2 outputs feeding each engine
1 output deeding the Genny
1 off position

But, obviously, only you know the accessibility of your vessel and whether or not it will accomplish what you want it to do.