Am I being a bitch?

We're getting married next summer and now so is sil. The day day we got engaged we saw partners side of the family and sil new boyfriend made a comment about their wedding (they weren't engaged) baring in mind they'd only been together about 4 months it annoyed me as I felt like the shine was taken away from our special moment. Recently he proposed they've just been together 1 year and he's already divorced from someone else. Now they're wedding is happening just a couple weeks before ours even though they knew our date so same month I just feel like every step they try and 1 up us on everything to take away our moment. Realising now she's actually always this way about everything very much an attention seeker partner and her don't get along well because of it. Now we've asked for some help organising some bits for our wedding from mil and she's said she can but it'll have to wait for a while until his sister has been sorted as she's asked the same. I feel like everything about ours is going to become 2nd place. I do like my mil but she definitely treats her daughters very different to her son's and that does annoy me and partner. I did first try to make it bond us that we could wedding plan together etc but it's been made clear she's not interested in that Am I wrong for feeling like she's taking our special moments? I haven't said anything to anyone to make sure I don't cause a problem but it's frustrating