Void agreements involving marriage

Dear PAO,

My cousin and her husband have been married for 17 years, and they have three minor children. However, they are no longer together. Her husband now has a girlfriend, and my cousin has a lesbian partner. They "separated" because her husband cheated on her five times. Her husband wants to remarry and since they now have their own lives, they both agreed to live separately and even made an agreement before the barangay that they will now be terminating their marriage and declaring it as void or annulled. Is their waiver / compromise agreement valid?