It is my understanding that the BMS only protects the battery cells from over or under voltages - there may be some out there that can handle connecting/disconnecting a pair of battery packs safely - I have never researched this.?
my guess is you can find a Victron BMS that can communicate with your Victron charger/inverter. This would be a good thing.?
if space requires use of pairs of smaller cells, I’d suggest you build the pack with pairs of cells. As mentioned, each pair would be treated like a single cell by the BMS. If a pair is out of spec, you’ll have to unwire and test the cells to see which one is faulty. I’d suggest you buy a couple of extra cells to have handy for replacement or just take the pair out of the string and run 15s until you can get replacement(s).?
Reuben Trane