Can my stepdaughter's biological father get stationed at our base so he can still see his daughter?

If there is a slot for his MOS available yes he could. But there is no guarantee. Just because he has a child there won't guarantee, especially depending on the custody situation. But it all depends on the Army's needs.

Sergeant, I would say: not necessarily. And, I am so sorry that I have to divulge that to you.

It’s possible that he could possibly get a compassionate reassignment as he’s leaving AIT but it would depend heavily on the commander, his platoon Sgt would likely have to be willing to “vouch” for him for lack of a better word and it may require some luck. If you chose to remarry he could be stationed where you are and then you could get the marriage annulled.