Can I bring my mother or a close friend with me to my husband's polygyny hearing?

You can bring them to court for support, but whether they may enter the judge's chamber depends on the court. Hearings of polygyny applications are usually not open to the public. Your lawyer can attend with you; for anyone else, ask the registrar or politely seek the judge's permission. Even if they only wait outside, their presence still means a lot. Choose a companion who calms you, not one who is quick to anger or likes to argue with your husband and his family in the court grounds. Tell her what you need: company, someone to listen, or a lift home afterwards. See hearings in private.