"one battery only, but I was wondering if I could hook two batteries up parrallel as one bank,"
Sure you can. Remember, a "battery" is a collection of CELLS. If you combine them in series, parallel, or series-parallel, it is still ONE BATTERY.
A battery bank is simply a collection (an ordered group or array) of cells that have been assembled into "sub" batteries within the bank, but as long as there's one big terminal at each end, that "bank" is still just one battery of cells. Same term, same usage, as a battery of cannon.
At 6A capacity, it may take longer to charge the two batteries. And if the batteries are of different age or condition, you may find one is under/over-charged as compared to the other, unless you charge them separately. But you certainly can try, those issues with combining batteries would apply regardless of the charger you used.