Dawn, this is very much something you need to work out with your lesbian daughter, as it is her wedding, but there are a many ideas and resources online to help you. I would suggest you search on terms such as “planning a gay wedding” to find help. There are books, articles, and websites focused just on gay weddings, with ideas, resources, pointers to venues and vendors, and possible challenges addressed (such as invitation lists). With the legalization of gay marriage, there is an industry around gay weddings, so let those resources help you. Much of the online information is free and knowing what others have planned or done can help.
Bear in mind these two weddings would probably be different in any case, as what your two daughters prefer will almost certainly differ. Couples choose many varied options, so this may pose fewer challenges than you fear. Make sure any venue or vendors are happy to work on a gay wedding and that guests and family are aware you are happy and supportive. Much of the rest is, as always, finding out what your daughter wants within the scope of what you can provide.
The issue of non-accepting family is touchy. If your daughter is aware of those family opinions, she has many options. She can alter her invitation list. She can invite everyone and let the negative RSVP come from them. Or she can find a middle ground most comfortable for her and her fiancé. Her future partner may have the same issue, so they will likely work through this together. Ask what they would like and how you can help. Now that your daughter is an adult and the topic is her engagement, you can defer to her preferences of whether, when, and how you communicate with extended family. Much of this decision is theirs — like any bride or engaged couple, they get to call many of the shots.
However, if she is not aware of some individuals who disapprove, it is important that you inform her. Be as specific as you can about what they did or said that has you concerned. That can be an unpleasant role, but it is important to let her assess what she wants to do. Sometimes people have hostile opinions that melt away in the face of someone they love. You can offer to touch base with a relative or friend to feel out their thoughts if your daughter would like that. In any case, be prepared to answer later if you get any pushback around “why wasn’t I invited”. Your role then is to stand up for your daughter without apology.
Finally, congratulations and best wishes to both your daughters, and to YOU for offering love and support.