[{"id":"room1","members":[{"id":"member1","acks":"XXX",},{"id":"member2","acks":"XXX",},{"id":"member3","acks":"XXX",},{"id":"member4","acks":"XXX",}]},{"id":"room2","members":[{"id":"memberA","acks":"XXX",},{"id":"memberB","acks":"XXX",},{"id":"memberC","acks":"XXX",},{"id":"memberD","acks":"XXX",},{"id":"memberE","acks":"XXX",},{"id":"memberF","acks":"XXX",}]},{"id":"room3","members":[{"id":"memberX","acks":"XXX",},{"id":"memberY","acks":"XXX",},{"id":"memberZ","acks":"XXX",}]}]

db.collection.find({"$or":[{"id":"room1","$and":[{"members.id":"member1"},{"members.id":"member2"}]},{"id":"room2","$and":[{"members.id":"memberA"},{"members.id":"memberB"},{"members.id":"memberC"},{"members.id":"memberF"}]},{"id":"room3","$and":[{"members.id":"memberX"},{"members.id":"memberY"}]}]})