BMS for multi cell batteries
The multi battery balancers will work, and provided you use the same type and number of cells connected to each similar should not cause issue, if they have different numbers of cells the imbalance in power consumption from the balance PCB's will cause an imbalance on there own, 

however treat each like a separate 14S battery in that case, if they have any data or status lines, keep them separate. e.g. via opto-couplers if you need to drive something on another PCB.

Charge rates should be kept in the same order of magnitude of the balancers per cell current limit, if old cells are used, keep it closer to this rating, 

If the boards have status outputs such as charged, flat or balancing, I would make use of them to allow you to ramp up your charge / discharge rates if you need it.