I'm glad they hatched. I would definitely put a calibrated thermometer or three inside your incubator for the next hatch. I'm pretty sure your temp was a bit low.
Day 20 is getting pretty late for buttons. I would candle to see if any are still alive. If they are, it sounds like your incubator's temperature was a bit low.
Your second pip looks good.
As for the one pipped at the wrong end, if you see the beak sticking out and it's moving but not making progress, it probably needs help. Be aware that most chicks that have issues hatching are having problems for reasons. It might not make it even with assistance...
You should have a hygrometer in your incubator as well as a calibrated thermometer or three. Unfortunately, incubators lie about temperature and humidity.
You want the humidity to be around 70% for buttons at lockdown.