I'm not sure if I should address them individually or as a pair
Sehr geehrter Herr und Frau Schmidt or Sehr geehrte Pfarrer Schmidt
German Language Stack Exchange is a bilingual question and answer site for speakers of all levels who want to share and increase their knowledge of the German language. It's 100% free, no registration required.
Sign up to join this communityThe most common way to do this is
Sehr geehrte Frau Schmidt,
sehr geehrter Herr Schmidt,
If you don't want to specifically adress them in their capacity as pastors, I would leave the "Pfarrer" out.