You can charge 2 x 3s packs or 3 x 2s packs in series
As long as you have the correct charging / balancing cables you can charge multiple packs in parallel
There are some precuations when doing so
Packs need to be the same cell count and close to the same state of discharge
How quick they charge will be determined by the charging capacity of the charger versus the size of the packs
Cheers