How many BMV-712 Smart devices are required

Good morning I am looking at a small system design. House 2 x 200Ah LiFePO4 in paralel and 1 x 140 AGM Engine on a seperate circuit. How many BMV -712 Smart monitors are required? Two or Three? i.e.
1 or 2 for House and
1 for for Engine.
If it is 1 for the house, will this monitor be able to provide information on each battery seperately or for the two combined. If it is the latter, then my undestanding is that 2 are required to provide the best information.
My apologies if this is a stupid question. I am trying to learn. Thank you.

Normally you only monitor the house battery for current charged and discharged to give you the state of charge (SOC). Your 2 house batteries are connected in parallel so act as one large 400Ah battery and need 1 BMV. The BMV has an auxiliary port that can be connected to the engine start battery to monitor the engine battery voltage, but not the current or SOC. This is the usual set up using 1 BMV.

It is possible to put a 2nd BMV on the engine battery to measure current and SOC but this is not normally done.

Good day, thanks very much for your advice, much appreciated…