Let me start with I am a gun owner, and finish with it is illegal to discharge a firearm within 500' of another person's dwelling unless doing so for self defence in all of New England. The only state I don't know for fact is Maine, but I would assume it is this way just about everywhere with all the antigun laws now.
Be very careful, anyone shooting in such a reckless manner is very dangerous and unfortunatly I think your two boys are probable wise to be as afraid as they are.
Please don't tie your dogs out it makes them a very easy target, try to make a solid fence either livestock mesh or chainlink setback along your property line or if you can afford it a privacy type fence.
Finally I don't know what the police situation is in your area but if you are affraid of this guy and I think you should be, consider going to the next level. For us it would be the state police, even try talking to the local chief, just be sure it is documented.