Okay you should probably sit down for this one.
Backstory- My FH has a "sister" who lives with his mom and godmother. When he was little his dad was removed from the picture and his mom moved in with her best friend and his godmother. His godmother had a baby girl and shortly after she was born her father passed away. So basically it's been these two bestfriends living together and raising their kids and it's always been that way. He has always referred to his godmothers daughter as his 'sister' and she's always referred to him as her 'brother'.
His 'sister' was born with Down Syndrome. If you didn't look at her, you wouldn't know she has a disability as she is very high functioning. She is smart, and knows exactly what she is doing to manipulate others. If her parents put her in classes she could take care of herself for the most part, but they don't. Her mom, and my FH mom have always made excuses for her such as "she doesn't understand because of the Downs." This has caused her to be a full on brat. She is mean, and rude, and needs to be the center of attention at all times, she is basically a bully. She has always been especially mean to me because "I took her brother away from her" This causes a rift in our relationships with his side of the family. I've expressed my concerns regarding her behavior for our upcoming wedding and they basically push my concerns aside by saying "don't worry, she'll be fine." and "we don't understand why she can't be involved more" Even my FH has explained to them what is expected of her behavior for this event. Well fast forward to now, my FH and I have been together 8 years and are getting married in October 2021.
They have yet to ask my FH what they can do to help him out with the wedding or if there is anything they can do to make him happy. It's always all about his 'sister'. They requested she be a bridesmaid- I politely said no because we have a very small bridal party consisting of my sister and his best friend of 15 years. They then asked if she could wear white to match me... I obviously said no but I took her to David's Bridal and helped pick out a "special" dress just for her. I even made her a bouquet so she would feel included. They asked if she could have a special glass at the reception with her name on it like my FH and I and I said that wouldn't be fair to everyone else and that the glasses we have for everyone else is fine for her too. They requested a 'special' brother sister dance to happen at the reception directly after our first dance- I told them absolutely not as this isn't a thing that happens at weddings and it wouldn't be fair to any of my siblings? They wanted her to walk down the aisle behind me and carry my dress and I said no, we aren't even having a flower girl or ring bearer. I made her an usher to help make her feel important, she will be ushering her mom, my FH's godmother to their seat. It was at this point they thought if they asked my FH and not me that they might receive a different answer and my FH explained to them that "what I say, goes." This was of course after they tried to say I was being selfish and unfair to his 'sister' in her "condition".
The last straw was that they are asking we allow them to invite a 'date' or 'friend' to come as his 'sister's' sitter for the day so they can drink and not be obligated to worry about her being a brat. THESE WERE THEIR EXACT WORDS! If you know how she is acting- why not fix it rather than make thousands of excuses and ignore it.
I have taken every precaution in planning this wedding as to not 'upset' anyone but this is OUR day and I don't want her to cause a scene because eyes aren't on her. My FH is concered and embarrassed as well. We don't know what to say or do at this point. HELP?