One of the most important lessons we have to learn is that we can't control other people. If your son and daughter want to fight then that is their decision. Go to his wedding in the same way you went to your daughter's wedding. Your going does not mean you approve of what is going on. Your going just means that you want to be there for your son's wedding. Going to the wedding does not mean you are taking sides.
As for you birthday, face it...sometimes people are just insensitive. You don't have control over your sisters, mother and brothers but you do have control over yourself. If you think you will enjoy going to your brother's birthday party, then by all means ...go. If you aren't going to enjoy yourself, then do something else.
As for your house...if you are like me, having a mess around me depresses me.
laughing at myself....sometimes when the house gets me down, I pick one room to clean up completely. I keep that room clean. That is the room that I will sit down in and relax. When I look around that room, I get pleasure out of being there. At times like that, I don't worry about the rest of the house. After awhile, you find that your energy comes back and you are ready to do something with the rest of the house.
One of the biggest things that can depress us is the idea that we don't have any control on what is going on in our life. Your going through that with your job, your children, and your extended family.
Cleaning that one room gives us some control. Recognizing that we are not responsible for other people's happiness also helps us to let go of trying to control everything with other people.
There is a good book called "Boundaries...When to say yes and when to say no" written by Dr. Henry Cloud and Dr. John Townsend. It really helped to change my life in the way I dealt with my sibblings, parents and friends. You should be able to borrow it from your local library. If you get a chance, read it. It will help you to put up your own boundaries up in dealing with your outside family.