That's not right. It's possible to do with just a single search; you just have to seed the open-list with all the enemies, what you've done there is to do many searches with an open-list seeded with just 1 entity each time. It's a variant of breadth-first search called Dijkstra's Algorithm.
The top-left pathmap is a breadth-first search for one of the enemies (in red).
The bottom-left one is a breadth-first search for the other enemy.
The pathmap on the top-right is the sum of the two searches.
Is this what you meant?
The free cells immediately surrounding any entity should have a distance score of 1. Take a closer look at Dawoodoz's example.