How Do I Charge, and Maintain 2 New 6 Volt Batteries???

Recharge them fully as soon as you are able. Running any battery flat shortens the number of times you can use it, but 6v golf cart batteries will tolerate this better than 12v hybrid batteries. You don't really get more amp hours out of 2 typical 6v than 2 typical 12 v batteries (very general statement), but they will survive the abuse for more cycles.

If you hook the positive on one to the negative on the other, the 2 open terminals act like a single 12v battery.

Jim