It is not so weird that the negatives have multiple connections. It is wrong and you should fix it, but almost every RV comes this way.
As for shunt, I have never seen the coach you have, but anywhere it can physically fit and be secure should be fine. I am surprised that the house batteries are with the engine. That's new to me.
2019 DSDP 4369 * FREIGHTLINER XCR * HWH ACTIVE AIR
NHSO (Newmar Hoot, Sevierville Original), Kindness Matters