I have a sister who is, now in Moharam she wants to go to Mosque for majlis but her mother in Law doesn’t allow that and her husband due to fear of his mother also did not allow her to go. What should she do in this situation? Should she take a stand and go to Mosque for Moharam or should she sit at home do azadari using online majlis etc ?

To keep the peace she should watch at home although islamically her monther in law has no right over her in this matter.