Refering to this post Entity Framework and multi-tenancy database design, the problem of multitenancy with tenant id propagated to multiple tables bringd issues with multiple cascade path.
Indeed in the post, an OrderLine can reference a Product belonging to a Company which is different than the Company of the Customer having the Order and this is not what you want (unless the same product catalog is shared by ALL companies but that is very unlikely in practice).
Therefore you may want to have CompanyID as part of the PKs so that when defining the FKs it ensures that the same CompanyID is consistent all the way down to OrderLine.
The problem is that you need compound key and not all ORM can handle it. Also this architecture starts to get complexe if you have a table that needs to reference itself (for example an Order depending on another Order).
To keep a shema simple while being able to overcome the issue mentioned before, I could only see a design like 1 tenant per DB.
But if somebody had a better idea is gladly welcomed.