The Cooper kids adventure

1. 

   Book 1

   The door in the dragon's throat

   Frank E. Peretti

2. 

   Book 3

   Tombs of Anak

   Frank E. Peretti

3. 

   Book 6

   The deadly curse of Toco-Rey

   Frank E. Peretti

4. 

   Book 7

   The legend of Annie Murphy

   Frank E. Peretti

5. 

   The secret of the Desert Stone

   Frank E. Peretti

Book data and covers from Open Library (openlibrary.org).