My son has ADHD,PDD and Sensory Integration Disorder. He is 8 years old. One thing I can tell you for sure is if you can communicate well with him is play detective and ask him what bothers him the most about having someone else in the house. I notice a lot of times I can sove problems by asking questions and talking things out to fix what is bothering him and triggering him off. My son is an excellent talker, but as you well know with this disorder, these kids can't tell us why they are upset. They have sort of crossed wires. It's in there, you just have to figure out how to get it out for them. Sort of teach him how to communicate. Always stay calm. If you ever notice, the second you get the slightest bit upset, I can lay money on it that his temper will escalate tenfold. If you keep calm and just ask questions, you will get answers and learn how to fix 80% of the problem. If it's not fixable, you will learn how to explain things to him that he can't understand. The more he understands the less frustrated he will be and the more orderly your home will be. Also, children like him are kids of routine. Get a routine and keep it going. If he is very strict, than that may be what is making him upset. If something is throwing him off routine than that is something you will need a therapist to help you with. Our routines are strict in the morning and at night, I never have to deal with mid-day routine problems, yet! Knock on wood LOL.
I strongly recommend that if you don't have an outside agency helping you, get one! We work with outpatient therapy, family based services, TSS, whatever we need when we need it for him and have seen him move mountains! I would go back and do it all over again if I had to. It's been a long hard struggle but well worth it. Take the most intense program and listen to what they tell you. Work with the people and let them guide you. They are trained and can help. It get's frustrating because in the begining you feel like you are the only one who knows your child and you try to protect them as best you can, but if you don't let them try to be as independant as possible in this world you will never have the peice of mind that you are so desparately longing for. I know that from experience.
We did dietary changes and it made a world of difference. Make a food diary and when he has the most mood swings. You will begin to see a pattern. Foods that are high in perservatives and artificial colorings and artificial sweeteners are the devil!! Stay as natural as possible. It seems impossible, but really it's not. Whole milk, natural cheese, nothing processed. Visit http://www.feingold.org and find out about the Feingold Diet. It's a real blessing. We also added supplements on a daily basis instead of medications. There are options, you are not stuck.
If you ever need to talk shoot me an e-mail. I've been there and still have those days, it's just a lot easier to deal with now.
Best of luck!
M.