Barb,
You cannot control how people feel about each other or how everyone else processes those emotional hurts (real, intended, or imagined). The only thing you can control is how you want to deal with the relatives.
Yes, it is sad that your DD probably won't be at your son's wedding. If you get in the middle, you may be uninvited as well. If it's meant to be, your offspring will sort it out eventually. In the meantime, you have a relationship with both of them.
If you feel that you are only invited to your brother's birthday because of an obligation, don't feel obligated to go - don't go if you don't want to. However, if you want to go, I'd say don't take your unresolved hurts with you, instead you may look at the gathering as another opportunity to reconnect with your family. Relationships have to be maintained, and it sounds like your family collectively is wrapped up in their own lives and that is OK.
I have been through it with my own family (my brother didn't speak to us for 7 years) and we have pretty much pulled away from Pat's family (too many nuts, sluts, and perverts - according to my DH). All I can do is figure out where I fit and where I want to fit. I'm glad that my brother is back in the picture but the in-laws will not ever be part of my life again - except for my MIL.
Can't say anything about the business other than wishing you a windfall of good luck and lots of inspiration.
Hugs from CA.