Am I being ridiculous?

I have a serious love-hate relationship with my soon to be MIL. She is a wonderful person but I dislike her as my fiance's mother. She is always putting us on the back burner and obsessing over his older sister. His sister got married right before we got engaged, and rather than be excited for us, his mom couldn't stop throwing his sister's marriage in our faces. She barely even acknowledged the fact that we got engaged. She's been super involved in his sister's wedding planning (they're legally married but had to postpone the actual wedding because of COVID19) but almost seems like it hurts for her to have to talk to us about our wedding. Now, his sister is pregnant. We have been talking about having kids for about a year now, but want to wait until after we're married but even so, she has always tried to talk us out of it saying we are "too young" and "don't know what we want" even though we've been together for four years, live in our own home and both have stable employment, but his sister is still living with the mom with her husband and they've only been together for about 2.5 years.
My issue here is that I'm not excited and barely happy for his sister. I know in the upcoming months all I am going to hear about is his sister's pregnancy, her wedding, etc. It's very hard for me...in early 2020 I had a miscarriage and it was very traumatic for me physically and my fiance did not handle it the way I felt he should and he also didn't want me telling anyone what happened, so I had next to no support during the weeks surrounding my miscarriage, so to watch everyone be so happy for her is hard for me to watch. To top it off, my mother passed away and I have no family left at this point, so it was always a comforting thought knowing his mom was kind of like a second mom to me, but now I feel like an awkward reject daughter and watching his mother and sister bond over her pregnancy and marriage makes me super upset, knowing I'll never have that. In my mind, it's easier to support his sister from a distance, but I told him I have no desire to be directly involved in her wedding (not that she asked me to, that's another story for another day) or being an aunt because it's too upsetting. He seems to understand fairly well but I can't help but feel like I'm coming off as a narcissist or a huge b-word. I don't plan on being vocal with anyone in his family about it because I know how it'll appear. I don't know if there's really a question here, I guess I just wanted to vent, but also am curious as to how others might react to this if in my same situation?

for context; I'm 26F & my fiance is 24M