Can NPC stop postulating in our squadron at some point?

[Mholito]

Just let the new recruits available pile up for a few weeks, and go through and dismiss the ones you don't want. Eventually you will have the one you want waiting for you to accept them.

You can only have one recruit from each category waiting at a time, and which one it is, is determined the moment you check the enlistment papers, so you can literally get the exact same twice in a row without even leaving the barracks.