Joshua Bardwell is a Quadcopter legend. His parallel charging boards are expensive but well worth it. They have 10 ports and fuses on BOTH the main lead as well as the parallel ports. I have accidently plugged a 4S into the 6S board (my 1500 mah 4S look identical to my 1250 mah 6S flight packs) and the fuse saved my ass. I have his boards in 3S, 4S and 6S.Charging several lipos on a Parallel Balance Board is ok if all the lipos are the same volts each pack, Same cell count, and all balanced well before charging.( 2,3,4 or 6s) You add up all the capacities and set your charger to the appropriate amps based on total of all capacities. That's fine. Make sure and use only a QUALITY bal. Board. The Chinesium stuff will fire up/ burn. trust me, Been there.
I use a Joshua Bardwell Signature bal. board (Fused). ISDT makes a decent one also.
Maybe others do it differently?? Most of my 6s packs are between 5500 and 6500Mah. They are fairly close in capacity anyway. Using a 24 400wat PSU D6 Duo. 2 of them to get many packs done faster.
He has a bunch of videos on charging lipos, testing lipos and even "breaking in" lipos. I highly recommend his YouTube channel and it is a must watch if you want to get into FPV drones.