Got a common sense question: If you ask a person to buy a key lock for a door what type of lock would you think they asking for?

Nope your right i would say that a key lock is a lock which is locked separately by a key like shed doors an things a slide lock isn't that good can be opened an shut from outside with a little effort an a pair of pointy nose pliers or scissors

Guy bein a guy...you don;t understand the brother is question has mental problem. So parental skills have nothing to do with it and if that was the case then correct me if I'm wrong he a parent too. And it apparent you are have relationship problems if you first instinct is to assume it about parenting. I understand fine because anything that need to be fix had to be fix by me. He will not be putting the lock on the door I will. This about basic knowledge and tell this is not a common sense question that the average guy would not know this.

a lock in which goes over the knob of the door in which only a key could open. You could save yourself some money by just buying a latch and a small key lock

Except for bathrooms AND the master bedroom it is uncommon for interior doors to contain a lock.

The problem is not the lock, the problem is you still berating the ex for something you yourself do not understand.

That, and the brothers who do not respect personal space and property.

Maybe you should work on your parenting and not his "mechanical incline".