You can charge the 2S batterie packs individually. I don't see why it would be necessary to charge them in parallel. One thing to consider is that one battery pack may discharge differently than the other, so you may need to set your LiPo cutoff a littler higher than with a 4S pack. For example, pack A is at 3.0V but pack B is at 3.2V, which means together they're outputting an average of 3.1V. If your cutoff is set at 3.0V, it won't kick in until the average voltage for both packs is 3.0V, so pack A may drop below the minimum recommended 3.0V discharge level. So as far as LVC, a single 4S pack is easier to deal with, but dual 2S packs gives you more flexibility if you have other vehicles.