Is this the worst bridesmaid dilemma ever?

‘Hi! Thanks for reading this. There's aloooot of Wedding drama history between me and my MIL (would make for a great sequel to that Monster in Law movie) that I could go into if anyone was really interested in a long Wedding rant to make you feel better about your MIL - but to set the scene myself and my husband got married almost 3 years ago now, had an absolutely phenomenal day and have an incredibly happy marriage which is what it's all about right?! I thought that's where our Wedding story would (and should) have ended, on a happy high note and everyone would get on with their lives.SIL is now getting married, and I'm genuinely happy for her and her fiance. However, I've had to sit through family get-togethers recently at which they've been unbelievably condescending and straight up mean about our Wedding so I find myself still defending my Wedding decisions to MIL almost 3 years later which makes me feel ridiculous! I've grinned and taken the hits thinking 'I had my day - this is their time - they're just a little insecure because all of MIL's friends go on about us having had the 'best Wedding ever' etc etc but I feel like I'm all out of patience and not sure if I'm being oversensitive and silly.I'm a professional musician and SIL asked me to play her down the aisle, so I was like yes, no problem I can do that for her (even though they all know I don't enjoy performing that sort of music). At dinner the other night MIL says she needs me to play at arrivals too - DH and FIL both speak out and say something to the affect of 'she's family she wants to enjoy the Wedding and not be working' but I again grin and agree and take the hit, let's not make things awkward. MIL then says 'at least you'll get a free dress' which is obviously news to me! Turns out they want me to wear the same dress as the bridesmaids. This makes me feel a.) like it'll seem like I WANTED to be a part of the bridal party but didn't make the cut so as consolation they're letting me wear the dress and b.) a bit like I'm being treated as part of the furniture/hired help. I have taken into consideration that it may indeed be their way of thinking they're including me in the wedding in some way, but again it feels really condescending; it's not like they're wanting to dress my DH and he's their son/brother!I was a ridiculously considerate bride and regret it to a point because I chose to please MIL and rather hurt my own Mom's feelings to keep the peace during ours - also SIL was one of my bridesmaids and I gave all of my girls the freedom to wear something they were comfortable in - so I feel like this is all an unbelievably inconsiderate thing to do as I really should just be treated and left to my own devices as a guest like everyone else.Am I being over sensitive? Is it normal to expect your SIL to wear what you want her to to your Wedding if she's not a bridesmaid? (make no mistake I have no interest in being one and it's not like I would have worn white or anything) As the bride to be how would you want me to tell you that I'm not comfortable with this?TL;DR: MIL & SIL want to dress me (in the same dress as the bridesmaids) for SIL's Wedding, I'm not part of the bridal party and don't want to be dressed by them, just want to attend the Wedding dressed suitably as any other guest. Am I being ridiculous? As a bride-to-be how would you want me to tell you I'm not comfortable/happy with this?’