Honestly, your family has let your Aunt establish her residence in her mother's house. This could very well be a legal issue.
I think that before you do or say anything, have your ducks in a row and speak to an elder attorney or someone knowledgeable in the laws regarding this.
This way, when Aunt comes back to you says, X, Y, Z, you will already have an answer to her replies and you can state so with conviction and knowledge on those answers that you give, stating that you have already consulted with an attorney.
This will make her see that your family is truly serious about her being out of the home.