1- As difficult as it sounds, pray fir your brother in law’s wife. Praying for her will help in removing jealousy from your heart.
2- Remember that what really matters is how Allah views you. As long as Allah is pleased with you and you are trying to obey Him, that’s what counts. Your mother in law’s treatment won’t make you a better person, won’t help you in the Hereafter, or won’t help you spiritually.