This. Basically you need to assess how strong of a case you can make to law enforcement and how anonymous you can remain to your criminal neighbors. There is such a thing as anonymous tips. However, should photographic evidence be shown to your neighbors, and they recognize that the point of view is from your property, then you have a problem. Even so, once criminals are arrested I think your odds of having to worry about them decrease, contrary to your natural concern that they will retaliate. Retaliation takes effort. Planning, committment, investment- things these people lack to begin with. Once they are sitting in handcuffs getting dragged into court and serving time, they're preoccupied with other things. For one, they are probably using drugs, which means they have an ongoing motivation to obtain drugs. This is a drain on their resources of time and money. Next, they probably have people with whom they care about maintaining contact, and sharing time with. More time and money spent on that. They will have all kinds of financial problems to deal with if/when they get out, which is again going to reduce the time and money they have to spend coming after you. Survival for poor people is hard enough, but it's even harder when they are addicts who are lazy.
Hopefully the owner of that firearm reported it stolen. That would drive the nail in the coffin for that 13 year old, although his pops may take the heat for him if it is simply found "in the house." Being 13 he may not get as lengthy a sentence as if he were an adult, but still, it isn't going to be pretty if he winds up confessing he stole a weapon. If the dad is the violent sociopath who is killing animals then maybe the son is less the one to worry about anyway. To quote GOB from Arrested Development, "Under 18...walks out clean!" is unfortunately sometimes far too accurate. I knew kids in high school who got arrested for things they should have served time for but instead they received a slap on the wrist. This is a possibility, but remember the father is a straight up drug dealer. At any given time there is probably a sufficient amount of drugs in the house to get a possession with intent to distribute charge at a minimum. Hopefully a lawyer could chime in on the sentence he is looking at, but use mycase to look up his record. If he already has a rap sheet... I say go for it. He won't be a problem again anytime soon if it is something harder than pot.
As for your parents' say in this, ultimately you are an adult. I'm not saying not to respect them, but in one sense 18 is just a number. You conduct yourself as an adult on this forum and as such I know you are thinking long term as to the consequences of your decisions. There is the very responsible concern that harm could come to your family by taking action against them, and you want to avoid conflict. Of course you do, you're the good guy here and you want a positive outcome. At the same time, you also don't want a stray bullet to come through the wall because Mr. Meth Dealer's 13 year old son discharged his 9mm through his wall, and then through yours, and an ambulance shows up for someone who lives in your house. Or, they could come over and steal from you some more when they're having a slow week peddling smack. They could decide you looked at them wrong like you might narc and then they kill your dog to send a message. I don't know these people so who knows, but you have already described sociopathic and violent behavior. You're also looking the other way on criminal affairs that are perpetuating a problem in your community. I'm sure you feel conflicted about that and you've already thought this through a lot. What I am saying to you here is don't be afraid to take action. If anonymity + action is the path you would like to take, then devise the most elaborate plan you can and carry it out. Use your smart phone or ipod or whatever to record this kid running his mouth. Get all the blabbing of his you can saved as an audio file. Take pics of these cars' license plates as they come and go (but be careful not to be spotted). Put together an "evidence package" with a $10 USB thumb drive and a professionally typed letter and sign it "A concerned citizen speaking on behalf of his scared community." Identify this guy by name, describe the gun (make/model), specify the date the dog was killed and whose it was, obviously the address of this house, the type of drugs you think they may be dealing- details will sell this. Mail it to the IMPD narcotics task force and voila, your neighbors will have a bad day when the police get around to looking into it.
I would be as thorough as possible though. Particularly detail the sociopathic behavior- trespassing, stealing, unscrewing light bulbs to mask their activity, killing animals, waving around guns in the back yard, etc.
Will these people get off the hook and then try to come kill you or your family? Statistically, it is very unlikely. It is a tough balancing act though... a witness testifying against them may earn them a much more serious sentence, while doing it anonymously may not yield the same results. At the same time, that testimony could put you on their radar when you would have otherwise been fine.
Maybe crimestoppers is the way to go. Just say that you have repeated watched drug deals happen, money being exchanged for drugs at 123 Criminal Way and that should be enough to get a knock on their door. I wonder if crimestoppers is able to obtain warrants so that they can show up and surprise them, rather than investigators talking to them and providing room for them to clean house before they ever get searched.
Well I did some reading about crimestoppers, here is the page, read it and see how you feel about it but I am leaning towards this:
Crime Stoppers of Central Indiana
Okay man, here is the actual submission form, you can submit it online:
https://www.tipsubmit.com/webtips.aspx?AgencyID=655&DSID=655
What i suggest though is that you discuss this with your parents. Communicate to them that you are very concerned and that you feel that as a family you have a moral obligation to do this, especially since there is no threat to you if the tips provided are so non-specific that the dealers would never know it was you specifically. I am fairly certain that in all criminal trials a person charged with a crime has a right to see the evidence against them. That being the case, every bit of your submission may be viewed by them at some point. The trick is to write it in such a way that it could be any of your neighbors and they would never be able to tell. Be careful not to say anything that would suggest that it must be you.
Doing it that way, they may have their suspicions as to who it was, but they will never know. And they won't risk a life sentence (killing you guys) if they aren't positive it was you. Do whatever you think is best, but there are many options here ranging from a coordinated neighborhood effort to make their life of crime difficult, all the way up to narcing on them and taking the witness stand against them. The more moderate option is crimestoppers.
Just remember...
"All that is necessary for the triumph of evil is that good men do nothing."
-Edmund Burke
Good luck, and props for coming to the community here with this problem for advice.