Design a BMS (overdischarge protection)
I answer myself. Maybe I am wrong, but this is what I have understood:

All MOSFETs are equal. I have seen it wrongly.
About the OC and OD protection, the same as above. I have seen it wrongly. The MMBT3904 transistor is off all the time like all the MMBT3906. When the Batt1 enter into OD protection mode for example, the MMBT3904 will get about 5 mA at it base, discharging the MOSFET bases disconnecting the batteries from load. When the other batteries enter into OD protection mode the current is lower, but looks like is enough to send about 0.18 A through the transistor and then again discharge the base of the MOSFETs. On OC protection is almost the same, but the currents through the transistors is a bit higher because the batteries have more voltage.

Best regards.