Ken
Hard to know unless someone has direct KVA experience (which I don't - sorry) but as far as your fuel levels are concerned, the sender units within your tanks seem to be the problem. One may not be working (check your wires going to the senders and also your fuse box as you may have a blown fuse) which will mean you may have to drop your fuel tank to get access to it if you don't have an access hatch on your sill. If you do then take the hatch off, un-screw the sender and carefully remove. Ensure that you protect the opening from debris falling in. Also note the orientation of the sender unit as you remove it because you will likely have to do the same to the one that is working.
The problem with these senders is that the float/lever action is compromised by the curve in the tank, as the level drops the float touches the curved edge of the float thus rendering the guage inaccurate. You will need to bend the float wire around to avoid as much as possible the sides of the tank.
Well that is how it is on my RF tanks and they are roughly 35litres each with another 5-7 litres in the swirl pot.
As far as why the tanks aren't linked, I know mine are serviced by a low pressure pump that supplies the swirl pot which is then drawn by a HP pump to the fuel rail on my injection system. The tanks are switchable of course, so only one LP pump works at any time. My return fuel line goes back to the swirl pot which then has two lines back to each tank via a switchable valve so that the fuel is returned to the supplying tank. Make sense??
I've been given different reasons for this setup, 1- during race can help adjust balance of car, 2- in case of failure in LP Pump 1, there is a back up system (not so sure about this), 3- "it is a race setup" (very simplistic reason...)
There may be more...
Hope this helps
Bill