Grandparents and Third Parties: Stepmother is Intruding on Mother's Role

My question involves a child custody case from the State of: Minnesota.

I share a 5 year old child with my ex-boyfriend. I have sole physical custody, he has specific hours of parenting time. We share legal custody. He is married to another woman. For the past 5 years, I have not had any personal dealings with this woman at all. There have been times where I suspect she was the catalyst behind certain issues between my ex and I, but she's never been directly involved. She's never attended any medical appointments, school functions, conferences etcetera.

About a month and a half ago, she showed up out of the blue to my daughters kindergarten conferences and made things very tense and awkward. She was telling my daughter to call her "mom" in front of me, and when I corrected my daughter she essentially told my daughter not to listen to me and she could call her mom if she wanted. I asked my ex to reel his wife in as I felt she was being very disrespectful, and he essentially told me to "grow up and get over it." The next day when I saw her father again I mentioned that it was inappropriate how she acted, and he told me that it was none of my business and it was up to my daughter to "choose" who she wants her mother to be.

Since then, my ex has cut off all communication with me. He refuses to answer any emails or texts, has been withholding her schoolwork and school papers from me after his weekends with her, and being generally unpleasant to deal with. We share legal custody but I cannot communicate with him at all to effectively co-parent.

Two weeks ago I found out his wife took my daughter out of school for what should've been his scheduled parenting time and had her for the three days that I was under the impression that she was with her father. In fact her father was not present and in reality I had no idea where my daughter was or who she was with (but didn't know that until the visitation was over.)

I emailed her school to clarify that only her father should be removing her from school for his scheduled visitation. A couple days after that, stepmom sends a letter to the school trying to get herself added to emergency contact forms and as a person who has consent to take my daughter from school. Luckily the school called me and I prevented that from happening.

Now that I have prevented the stepmothers access to my daughter outside of her fathers visitation time, stepmom has started volunteering in my daughters classroom behind my back as another way to gain access to my child. This makes me extremely uncomfortable and I feel the contact is inappropriate because the stepmother has been doing things like telling my daughter to call HER mom and requiring her to call me by my first name when my daughter is at their house for visitation. She also tells her she must go by their last name (my daughter has my last name) when she is with them. They also encourage her to lie to me about the volunteering in her classroom, etc. I feel this is emotionally damaging to my daughter. She is only 5 and shouldn't have to be so confused about telling the truth, who her mom is, what her last name is etc. I need to take action because this has been going on since mid-October and I want to rectify the situation immediately.

Any advice on what my remedies could be would be appreciated. Restraining order to keep stepmom away from my child's school? No third party interference clause? Other ideas?