Irrevocable burial account; do I need to have a trust document drawn up by the bank, or should I seek legal counsel?

Hi, My Mom passed away, and my autistic brother had an irrevocable burial account at a bank that my mother created. The state of New Hampshire had it, and I just got it back from the state as I am the trustee for it. It was originally taken out in 2003. The banking institute does not have any legal paperwork that might have been drawn up on the original deposit date. I do have the original deposit slip. My question is, do I need to have another irrevocable burial trust document drawn up by the bank, or should I seek legal counsel? I might add the original deposit was done in Massachusetts, where my brother and mother resided but my mom and I moved to New Hampshire, and forgot to make yearly deposits so the state took it for a while till I found it.