You do your homework, no complaints there.
That jumper is probably to completely separate the coil from the control signal through an optocoupler. It looks like there are two optocouplers.
My schematic is based on active high relays, some are indeed active low. So need some modifications. The trick for latching a relay is that the relay, by being activated, makes the circuit that activates the relay.
The blue dotted part is inside your relay module itself - schematic is not the same but same functionality: active low signal.