How do you address invitations to a married couple when both are doctors and both are reverends?

Simply pluralize the title. For instance:

Drs. John and Malina Smith

1000 West Washington St.

Greenville, MI 48838

Dear Drs. Smith;

Or:

Reverends Phil & Phillis Phillips

777 Pearly Gates Way

Paradise, TX 76073

Dear Reverends Phillips;