[jcus]

The two behind the tag are house batteries, and are wired in parallel with the four in front of the drive wheel.

The next question would be, should I disconnect the disconnectable trays and use a four circuit battery tender, one circuit for each of those trays, one for the tray behind the tag and one for the engine batteries?  It seems to be asking a lot to expect one tender to handle all six house batteries.  I always have a tendency to over engineer things.

If you are plugged in why do you need a battery tender? Your inverter/charger should take care of all of them.

Unfortunately, I can plug into anything more than a 15 amp house circuit.  I have covered parking 15 miles from where I live, but no 50 amp circuit.  You do what you can in the valley.

Once you get your batteries charged up, your charging part of the inverter should not take more than 2 or 3 amps to keep your batteries charged up. On many inverters you can actually limit the current that the charger uses and also your max incoming current. Even if you do not use these settings, just make sure everything is turned off, and you should be okay. Make sure all your other equipment is turned off [ fridge, heaters, ac's etc] If you are using a separate small charger for your start batteries, it will not take more than 2 or 3 amps either.
Of course you will need an adapter to go from your 15 amp receptacle to your 50 amp shore power plug.
Most people do it with two adapters, 15 up to 30, and then a 30 to 50. You might be able to find a 15 to 50 amp adapter.
I often store my coach with only 15 amp 110 volt power and even run the fridge and aqua-hot [diesel only] as well.