Hi,
The monitor is a BEP Matrix DC monitor - so not a computer - monitors voltage for house and engine batteries, shows amps charge or discharge, and shows a percentage of remaining capacity. The solar panel has a MPPT Controller then to the battery. Seems to work okay, but I’ll move the negative to the shunt.
The shunt seems to have a negative from the house battery on one side and a negative from the engine on the other side of it, with a smaller wire heading up to the monitor - does that sound right?