I've never been asked this question. Can two trusts form a partnership? I've seen zillions of LLCs with trusts as members, but never a partnership with anything other than natural persons as partners.

Dolly, that would depend on 2 things - the authorities granted in the trusts and state law. I have seen partnerships with non-natural persons.

Agreed. If you don't otherwise, your bank should require a written partnership agreement as well. If this was "planned" by an attorney who mentioned partnerships or other business entities in the trust and then mentioned the trusts in the partnership agreement, it's a pretty sophisticated enterprise.

If, on the other hand, it's just something that some guys slapped together, the fact that they can do it doesn't mean you must open an account for them.