Fiance's Daughter Not Cooperative

My fiance of 6 years has one daughter that is getting married next year. Due to my never having been in this situation, I have asked her what she'd prefer I wear (specifically requesting what she was expecting per her chosen venue), which she replied with "I don't know! Lol".


That's not the only issue; I asked what time the wedding is because her father/my fiance had no idea, to which she also replied with "I don't know". I explained to my fiance that their venue, which he laid for, is booked. That is a block of time. She HAS to know the time. So he asked her, and of course she knew the time and told him, so she did in fact know the time (as everyone knows, the time of the event determines the chosen attire).
At this point I've been spending a lot of time reading up on wedding etiquette so I am proper in attire and whatnot. At this point I doubt she will reveal the chosen color of the bridesmaids, and she won't even share a photo of her dress with her father, so I'm pretty sure asking this question will result in getting nowhere. My fiance, whom will be wearing a traditional Father of the Bride's traditional tux told me he wants me to dress up to match his attire - so that is now settled, however this is not by any means going to be a formal wedding based on their chosen venue.
I am now concerned about other possible issues because she's one that likes to throw in digs about me via jokes that I fairly recently stopped ignoring because of the level of disrespect (the disrespect at all and in the first place) is unwarranted and unappreciated and I finally spoke up about it. That said, her mother also treats me the same because (long story short) I didn't appreciate being treated as an outsider after all these years and put my foot down, which my fiance had no problem with and actually seemed to appreciate and have a huge amount of stress lifted. They basically don't appreciate my presence and he goes nowhere without me, which was also the brunt of jokes more than once and at inappropriate times (example: at his mother's service and at the house, after she passed away). We are simply one of those couples that consider each other, we are very close, and we hold hands and sit together. He will get a plate of food or drinks for me, etc. For some reason, his chivalry towards me is something they apparently don't like.
Anyways, I fully expect other guests and family members turn their backs to me, to be ignored during conversations, to be left out of photos, and who knows what else (yes, this is actually probably very likely to happen due to what has been done to me thus far).
I can say that I know with certainty my fiance will not allow any disrespect towards me, though he is sometimes oblivious that it's happening because, as I mentioned, it comes in the form of digs as jokes about very specific things pertaining to me.
I'm seeking any advice, really. This day SHOULD be about their nuptials, and I can't believe I even have to make a post about this, but I'd rather ask for assistance so I can get some insight and advice and be able to plan and be prepared, and hopefully avoid the potential for any unnecessary issues or drama.