Sorry to hear Jackson's turning into a rowdy boy. I have a few questions:
1. Do you walk your chi's? If so, for how long?
2. Do you ask your chi's to do anything for their food/treats? (like tricks, asking "wait", "stay", "sit", ect.)
It sounds like Jackson needs more direction. Maybe he should be walked longer and asked to do more things, so he doesn't feel the need to assert himself over the girls. He needs to be reminded who's in charge, here! Neutered or not, all dogs will have a hormonal rush and a personality change once in their adolescent lives. With females it's less noticeable or common (not always!) but with males there's definitely a time when they start to challenge their surroundings. It's in their nature!
1. Think of something you want to accomplish with Jackson. Maybe it's something new, or maybe it's a behavior you want to change. He needs challenge and direction so now's the time! Put together a plan with everyone in the family involved, and work on Jackson's patience and attentiveness. Chihuahua's are very intelligent (in fact, their brain to body ratio is the highest of all breeds! Just a fun fact) and if he seems confused you need to rethink your methods. He may be stubborn, but be patient. This is the challenge he needs!
2. Feed separately for now. Work on helping Jackson understand that you're in charge of the food, and really use his food motivation to your advantage. Make feeding time into "Jackson Training Time". Teach him new behaviors or ask for calm attentiveness before meals. If possible, give him a long long walk before meals to help him "work for his food".
3. When it comes to snapping at treats, give the treat to him with it hidden slightly in your fingers, so when he uses his teeth to take the treat you can say, "No teeth" or "Take it nice" until he starts licking. Then you can give it to him. He needs to learn patience, and he needs to learn that you are the one in charge of food, not him!
4. Never underestimate the power of the leash. It is our most clear and sure fire communication line between us and our dogs. Maybe he should be on a leash again for a while around the house, taught to wait in places and not "run his territory." When he's calm or doing something you like, you can release him or give him a treat.
Hope this helped! He's a smart little boy, don't worry. Just be patient with him (he probably won't like the new routines because he's starting to like being in charge more, but just keep it up. Remember he's a small dog and if all else fails you can just pick him up!) Get a goal and work it! Good luck!