I would contact the Standesamt (Registry Office) in Weitnau as everyone is required to register their residency where they live and update it when they move. As you are not a direct descendant, they will not provide you with death records (less than 30 years), but they should be able to tell you if they are still living there.https://www.freistaat.bayern/dokumente/aufgabenbeschreibung/23666151111?plz=87480&behoerde=38885350763&gemeinde=644301873678
