She may have had the guns to protect herself against him.
As for his getting at them, possibly she didn’t keep them safely enough, or possibly he simply knew how to get at them. Very often people who seem totally nuts are very crafty. I’m sure he had planned all this in advance.
Yes, possible. The circumstances of how they were kept will probably be revealed in time so we can judge it then. Some sort of screwup is possible, an accident or another party who was unaware.
Do you think Adam may have been jealous of her students hold on her time and attention?