Question

IS IT ALWAYS NOT NECESSARY FOR BOTH THE HELPING VERBS TO BE TOGETHER .

LIKE I HAD ALREADY EATEN THE CAKE

IN THIS SENTENCE HAD IS NOT WITH EATEN

SO IS IT STILL OK?

Answer 1

Ya.It is absolutely ok.There is no compulsion or rule that Both helping vebs must be together.

Answer 2

It is perfectly correct.  ALso,  we introduce the word  "already "  in between the two verbs because we want to emphasize on "already".    We are saying about "eating"  but we are giving additional information "already"  - and that is supposed to be important.