My parents want to confront my husband about his polygyny application. Should I let them?

Let them support you, but you decide how far and in what way they are involved. Parents' love can turn into anger that makes things worse, especially if they meet while tempers are hot. Explain to them what you need: someone to talk to, help with the children when you go to court, or advice. If they want to speak with your husband, suggest a calm meeting with a respected mediator. The Qur'an teaches that when husband and wife are in dispute, “then appoint an arbitrator from the men's family and an arbitrator from the women's family” (Surah an-Nisa' 4:35). What is sought is a solution, not a victory. See telling your parents.