multiple entities/ownership - Single or Multiple ER Plan?

Basic structure - One corporation with limited staff owns two entities, each with their own EIN.  Neither entity has ownership  in the other.

The two entities want to set up a common PS plan, but they want one of the two entities to sponsor rather than the common owner.

Trying to figure out if this is a Single Employer or Multiple Employer plan?

Do I understand that you have 3 corporations A, B and C. Parent A owns 100% of sub B and sub C?

They want to have B be the lead sponsor and C be an adopting employer (or the other way around)?

If that's the fact pattern I don't see a problem doing a single employer controlled group plan.

If I misunderstood the fact pattern, my apologies.

If A also has employees you'll need to decide if they are adopting too or not and whether your document pulls in all members of a controlled group. If A has employees and you are excluding them, you'll want to make sure you still pass coverage.

you got it, and thanks Lou for that reminder about the company A employees.

I have a similar situation except no parent company.

Company A is 100% owned by an individual and has 3 employees (including the owner).

Company B is 50% owned by the individual and 50% owned by the individual's spouse (clearly a controlled group). Company B has 25 employees (including both of the owners)

Company A has had a 401(k)/PS plan in place for many years; Company B adopted Company A's plan effective 1/1/2021.

Next year, will Company A file one Form 5500 and include consolidated info for Company A and Company B. Or do Companies A and B have to file separate Form 5500s?

Combined.