If you say that the "reload NPCs" function is the one that crashes your server, then just don't use it and that's it! As far as I know, that function when a NPC is talking with a player, it makes the server crash, no solution possible.
Another solution could be, that when you want to reload something, first close the server (so that, players are kicked) and then reload everything.
If you sometime ever need to reload a NPC, just use the procedure I told you.
If the reload NPC function is not what crashes your server, then what is it ?