My first two strings are sharing one JK-BMS.
My original plan was to hard parallel the two sets of cells at each cell group. But that was just not practical. So the solution I came up with is a bit odd. The negative ends of the two strings go to a buss bar and into the BMS. The positive ends have separate 100 amps fuses before the disconnect switch, and then out through a class T fuse to the output. Then the 15 balance leads each have two 3 amps fuses. One fuse goes to the cell test point of each bank. The resistance between the two banks is quite low and is holding the cell group from one string in balance with the opposite string. And then the BMS can balance between cell groups. If anything goes wrong, and the two strings are off balance at any point, the balance lead fuses will pop quite easy. And that will cause a cell voltage error so the BMS will shut down. 30 fuses was a pain to wire up, but it all works nicely. The wiring is all easily able to handle the normal operating balance current. With the battery bank at rest, I have pulled out a few fuses and measured the cells, and they are holding perfectly balanced between the two banks.
When I built up the second pair of batteries, I did not want to deal with all the extra wiring and fuses. So I went with 2 dumb BMS units which ended up costing less than the one JK-BMS. And if one fails, I only lose half the battery bank. On my old bank, the one BMS is a single point failure which shut it all down from a bad plug on the BMS. On the new bank, it is two completely separate systems. They only join after the fuses and disconnect switches. Having done both, I like having separate BMS units per string.