**Just go out for a coffee and break the news. Excite them about your wedding and make them part of your happiness. After all they are your friends and they’ll be happy for you rather then being sad for themselves, might think about themselves at night for a bit but thats all. You weren’t going to be single for the rest of your life.
Also, I hate the idea of being informed about a party or a wedding through facebook or messenger. Come on, you can give them a call. People are worth a call. Ask them how they been, whats going on with them and then tell’em whats going on in your life. The whole notion of telling people through email or facebook or messenger is disgusting. Stay away from it. People will appreciate you more, if you put a human touch to it. 
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**This is a cold war and you’ll have to play it that way. First off, its your wedding so you’ll have to be the one in control and, above all, make sure you’re not ruining your experience. The excitement and happiness you have should be shared with friends and family and don’t hold back in it. As for people who’ll talk, you’ll just have to keep a positive attitude. They can’t ruin your day until and unless, you give them a chance to.
As for your friend, you’ll just have to be tactical about it. Think about her weak point, that you * hint * but not use against her. If you drop a hint, that would be enough to scare her off. If you take the offenses then its not going play out well.**
**I don’t think that should be an issue. Its your wedding and just like her, you have the option to include people on your day or not. One thing I would suggest you is that you’re starting a new life and you’re going to need well wishes then old feuds. Perhaps, the reason your friend couldn’t ask you guys to come was financial or some other difficulty. So give them a chance to redeem themselves. If you ask her to come and she refuses, its not going to hurt you but if she does come, you’re making a new friend and putting old feuds behind.
P.s. I read an email my best friend of 15 years sent me asking for help and I had stopped using that email address. In his view, I didn’t responded to his help request but in my view, I missed an opportunity genuiely. So give people a chance to redeem themselves.**