M., I am so sorry to hear about the diagnosis of your son. I know this is a difficult thing, especially with him growing and going thru puberty. As for the seasonal mood swings, those too are difficult as the changes in the season can cause a person to go change themselves. As for he not being able to help it, I don't neccessarily agree. Does he see an occupational therapist or family therapist? He should be monitored very closely at this age and they should have worked out a medication modification system for you to have when this happens to avoid this type of uproar in your home. He can learn to help some of it, as with any child they learn what behavior works,so some of these "seasonal mood swings" may actually be just tantrums every kid throws. I know many bipolar people. One is a CEO of a fortune 100 company and he has learned over time with therapy how to control himself, just like anyone else. The reality is that all of us would like to yell, scream, and run around the house destroying things, or just letting out frustration, anger and fear etc. I understand completely the " he can't help it" thing. My son has a verbal and learning disability. He has a hard time communicating spontaneous thought. So he is very quiet at times, especially when put on the spot and needs to explain himself etc. He at times throws fits, explodes, breaks his pencil, papers etc when he is frustrated. He has learned that while this is how he wants to respond, it is not OK and he has to learn what to do instead. It is working, it helps him so much and he is doing much better. If your son doesn't see a therapist on a regular basis, that UNDERSTANDS BIPOLAR DISORDER AND has other bipolar children in their practice. Also, a therapy group of other bipolar teens would help him immensely, to understand that he is know alone in this, there are other's in life with the same problems and frustrations. Your family should be in counseling as well. This is give you and your spouse help in how to parent both all of your children, how to help a bipolar child grow into a productive adult. It is possible for him to grow up, have a family and lead a "normal life".
As for your baby girl, preschoolers are tantrum prone anyway and add the admiration she has of her older brother and you have a recipe for disaster. He has to learn that he is " working on how to control himself just like she is. He needs her help to see someone who can and does control herself. explain what you do when you feel that angry. (i.e. pray, take a walk, get some fresh air, lay down for a minute,etc.) all people mimic what they see in life, not just children. I hope you continue to have great hids,and a a wonderful life.