Wesley’s mom, a main character, was initially going to be the ship’s teacher. They shifted her over to the empty doctor position without changing much about her. Then they made a new teacher who was also changed to be a bridge character, as the ship’s pilot.
While Riker and Troi are adapted from Decker and Ilea, Beverly was more extrapolated from yeomen Colt, Smith, and Rand.
Edit: specifically, their bios were mostly about a potential relationship with the captain, how competent they were (making them reasonable mates for him), and having the “walk of a striptease queen.”