Legal Question in Wills and Trusts in Arizona

Your questions are confusing me. First you state that your sister is co-trustee with a friend of your mother, and she is also a beneficiary. It sounds like you are mistakenly calling your sister a co-trustee, when you really mean that she is co-executrix of your mother's Will. If your mother had a trust, then your sister and her friend might be co-trustees.

A person can be an executor or executrix named in a will, and also be designated as a beneficiary, that is a common practice. The duties and obligations of the executor take priority over any rights that same person may have as a beneficiary.

A person making a will is not obligated to leave her estate to people in equal shares, even though she is leaving her estate to two sisters. She may have decided that one needs more than the other.