R.---I think you need to step back and cool down for awhile. Yes, it does sound extremely unfair as your parents have taken care of everything for your brothers. But, you don't share why it was you left home at 16. I'd only have to surmise that there was some sort of conflict at home. But, I don't want to assume too much.
You need to sit down and have a long heart to heart talk with first, your BF and see why it was he went and talked to your father before discussing things with you. Maybe he wanted to surprise you. How much of your history with your dad is he aware of? Then, when you know your BF's intentions, you need to talk with your parents. Maybe they just think that since you've always been totally independent, that this is the way you always want to be treated. From what you've shared here, there are just too many unknowns.
I do not know proper wedding etiquette when the woman/daughter has been living on her own and has children already. Not that it really matters if the parents and the daughter have discussed what they want to do and come to a mutually agreed upon plan of action. Again, not knowing what your relationship is right now with your dad/parents, I still have to think that to not invite him/them to your wedding, even if you have to pay for it yourself, would be a very sad thing. You and your BF have to sit down and determine what you are willing to do, for the sake of everyone involved.
I always tell my kids that we owe them very little, shelter, food, a loving environment. And there is much that they need to earn in the way of priviledges from others. PLEASE understand that I am not trying to be judgemental. However, this is where my thoughts went after reading your post. I am likely to be way off base. I wish you much luck in coming to a better understanding with your father. It is not healthy to hold a grudge, if it might come to that. Be well, D.