I am the trustee of an irrevocable family trust in my mom's name. Upon her death, the trust will be disbursed to myself and my sibling. Last year my accountant claimed it was a Grantor type trust and no taxes were paid. This year, I'm doing the taxes and I think I should file as a Complex type trust. The trust made $18,000 in dividends. If I file as a Complex trust, then the trust owes around $4K in taxes. Can I switch from Grantor to Complex? Should I do Grantor again? Thanks!
You should use the one your accountant used assuming your accountant read the terms of the trust.
None of us here have access to the trust document, itself, and it could very well be a grantor trust.
You indicate that "last year no taxes were paid..."
As a Grantor Trust, any taxes paid will be done on your mom's return. The grantor trust information will be included in your mom's 1040.
I agree with @Anonymous_ approach.