Depending upon their next worth, their estate plan may have one, two or three trusts. If you are the beneficiary of any or all of the trusts, their attorney would have copies and would likely give them to you to read. If your Mom is not the trustee of all the trusts, you could as the trustee for a copy.
This is ticklish I am guessing, or you could just ask your Mom. But bottomline, if you are a beneficiary, you are entitled to know what your rights and responsibilities are.
Hope this helps