I usually watch stuff to be entertained and not to nitpick, but.......
If, to your knowledge at the time, there is only ONE doctor left in the world, and you are having a baby that you do not know the outcome, but KNOW that you need a doctor, why would you send the doctor (who is also an old man) into the tunnels at all? Seems like he should have been left behind for the safety of everyone and future needs.
It also does seem like one could have opened up some doors, backed off to a choke point, made a ton of noise, and killed plenty of zombies to minimize the risk......