Inviting unsupportive family members

On the one hand, you really shouldn’t have anyone who doesn’t support you and your husband and will put a damper on the day at your wedding. On the other hand, it does get tougher with close family because they’re so tied to everyone else. The fact that someone is family is not an excuse for horrible behavior, however, so realistically speaking, what would she do if she attended? Would she just sit off to the side and ignore you (which if you’re having a bigger wedding, you probably won’t notice anyway)? Or will she be causing a scene/making other guests uncomfortable/trash talking the two of you the whole time? Honestly, if she doesn’t like you that much, what are the odds that she would even accept the invitation? Have you spoken to your brother about this yet, and can he have a talk with her about how she plans to behave if she does attend? Maybe if he knows how reluctant you are to invite her, if she makes excuses not to attend he won’t try to convince her. With all that being said, if she has been completely inappropriate toward you and/or is likely to do that at the wedding, then I would tell your brother first that you’ll be unable to invite her so they’re not finding out with the invitation envelope.

You said she doesn't speak to you and your FI and that that she barely speaks to you. Which is it? As long as she's civil, that's all that's required. Unfortunately, unless she poses some kind of risk to you or your guests they are a package deal. It's both or neither of them. Where does your brother stand in all this? Maybe she'll make an excuse and not attend, or maybe the invitation will be an opportunity to mend some fences. Why is she so angry with you and your FI?