We have an SMLLC that holds real estate, but is a disregarded entity under a Living Trust (complex trust), and does not have an EIN. Can I still make the loan to the SMLLC but using the trust's EIN? Or is this similar to a sole proprietorship where the borrower should be the proprietor (in this case the trust), and the grantor/collateral owner is the SMLLC?
Thank you in advance for your advice!

I would be treated like any other SMLLC. If the trust is treating it as a disregarded entity, you would use the trust's EIN for the loan to the LLC.

So to confirm, the borrower is the SMLLC using the EIN of the trust. The W9 they sign reflects the SMLLC and the Trust EIN. Then opening the checking account I can use that EIN for the SMLLC also. What if I already have a checking account for the Trust? Same EIN and two different names/customers?

No different than me, who has Carey Consulting LLC which is a disregarded entity. My LLC has no EIN and it uses my SSN.

Perfect! Thank you so much!!