It's already been moved
If you have 2 separate strings and connect them in parallel at the absolute Pos/Neg ends, then you should use 2 bms'.
If you have 2 separate strings and connect them in parallel at the absolute Pos/Neg ends "and" connect a balance lead across the packs to their respective groups, then 1 bms can be used.
As far as the load is concerned, if you pull a constant current of about 500mA or less per cell while they are connected in parallel, that should be fine. I would not go anymore than 1A surge/cell though
For the bms units selected, as long as the bms can handle the amps required under surge, you should be fine. If you get cheap chinesium units, they like to rate their bms units based on surge, not continuous (this also applies to their inverters/chargers/etc). So usually, for example, a 60A bms really needs to be down rated to about 30A continuous. 25A to give a margin of safety.
However, you can get around this by bypassing the bms for the over/under current over/under voltage protection and only use it for balancing. Maybe use it for charging purposes (so over voltage protection) and not use it for discharging.