<human>: Could you distill the essence of the text into 1-3 sentences?

My fiance's father cheated on his mother several years ago with this woman, "Sarah". They recently got married - like a few weeks ago, recently. She's a stone cold bitch to me. Physically turns her body at dinner tables so she doesn't have to look at me, talks down to me, always exclaims "Oh I went there!" any time I mention where I go to college as if I haven't mentioned it a hundred times. They also drink like there's no tomorrow - everything they do involves going to a bar and drinking more than even I would dare to attempt.

She has two young daughters of her own, and my fiance's father and her dote on them all the time. Mind you, my fiance is one of 3 siblings, and his father never thinks to try and include them. My fiance hasn't received a birthday gift in 2 or 3 years (it's not about the gift, but a card would've been nice). 

Any time we talk about wedding plans in front of his father and his wife, they always talk about how much fun they're going to have, how much they can't wait for the open bar, etc. I can already tell it will be all about them, like it always is. And for once in my life, I want something to actually be about me. I want to enjoy this day. I am afraid that I am biased because my abusive father cheated on my mom and then married his mistress too - whose name is also "Sarah". Keep in mind that my scorned mother will also be at this wedding - and this woman looks very similar to my father's mistress. Am I being unreasonable for not wanting this woman at our wedding? Or am I just going to have to get over it and invite her and try to steer clear of her?
<bot>: My fiance's father and his wife are both cheating scumbags who just want to party and get drunk; I don't want them (or at least her) at our wedding. Am I being unreasonable?