Translation:Instead of going to church, they are going home.
"in" is a two way preposition. It can either lead to dative or accusative case. If it implies motion it is accusative. It answers the question "where to". If there is no motion, it is dative. It answers the question "where".
"Wir gehen in die Kirche" - We're going into the church. Where to? Into the church....accusative case
"Wir singen in der Kirche" - We're singing in the church. Where? In the church...dative case
Hope that helps!