what can the family do if the Neice have taken all of mom's access. She just passed away in Nov.2020?

I'm assuming you mean ASSETS rather than access.

You need legal advice on this

Go to the County Courthouse and ask to speak to the Clerk of the District Court.  Tell the Clerk what is going on and ask to speak with the Probate Officer.  The Probate Officer will check things out and get back to you.  If there was no will or if property was not left in Niece's name, then Probate Officer will take control and settle the estate.  That could take a long time but at least the Probate Officer will immediately put a stop to anything wrong the Niece is doing.

This  not a Genealogical question it is a legal one and you or other family members should talk to an attorney.

Have the niece subpoenaed into probate court so that she can prove whether or not she's entitled to do so.

You consult a lawyer and bring charges if the niece doesn't have power of attorney. 

What do you mean by her 'access'?

And what niece?

This has nothing to do with genealogy. 

If you're trying to say that someone in the family has removed some of your mother's property without permission, you need a lawyer. 

Take her to court if her actions are not in accordance with the mother's will. 

At least get a lawyer to review the situation and advise.