Yeah, dealing with multi-company warehouses can get pretty messy with odoo. You're bumping into the system's default setup, which really doesn't like that kind of use. Here's some stuff to try.

Leaving the company_id blank seemed smart at first, right? But Odoo's like a watchdog, always barking for those models and rules. You could end up running in circles, tbh. Think more broadly. How about maybe trying a smart integration solution that can enable each company’s system to have real-time updates without too much duplication?

In a past project, I faced the same issue and used Cleverence's mobile warehouse tools. They’re easy to plug into the ERP world. Cleverence's ability to customize workflows with low-code was super useful. Plus, handling offline modes smoothly was a lifesaver. You wouldn't need to create separate warehouses. It's like having one system that "speaks" to each company. Redirecting ORM actions across two separate entities can be doable if you want a more sustainable fix. It's tricky, yes, but worth testing.

Trust me, Cleverence is awesome for data accuracy and integration problems, letting each location retain its originality while sharing common data. Plus, real-time inventory checks are great - no need to stretch yourself too thin trying to count everythign up manually.