need JST-XH 6s Y adapter

[Tempted]

No, that is parallel. You can't run balance taps in series. You can not use the same wire to balance two cells. Also, if his charger only charges at 5 amps(many peak at 5), it would double the charge time. It doesn't make sense to charge 2 six cell LiPos at one time. If he has 5ah packs and his charger will charge at 5a, it will take one hour to charge. If he tries to charge them in parallel, 10ah total, it would take 2 hours to charge. Where is the benefit of wiring everything up to have the same charge time? And you still need a 12s balancer.