MIL SIL out of their minds. A little long.

I'm pregnant with my first, due in December. My sil is pregnant with her 4th, due in September or October. My boyfriend and I went for the gender scan today and had the lady write it down. Then we went to a bakery and ordered a gr cake and put a payment down on it. We called everyone and told them we wanted to have it next Saturday. It's easiest for us and the majority of the people coming because everyone including us two are off from work. Everyone agrees until sil gets off work and reads her messages. She calls my mil and says we need to move the date and we're selfish and didn't think of her because she has to work: she wants us to revolve our day around her. Then mil calls and says cancel your order well order a new cake and have it ready Thursday when sil can come. Wat? No. We don't want it during the week everyone works. Then she says make it for Friday then. NO. Then she says well then have the bakery write the gender down and hand you the paper and then you give the paper to sil so she can open it while at work when you have the party... wtf is going on. My boyfriend spent an hour on the phone with her but wouldn't be direct and say this isn't sil in laws day it's ours so now I'm mad at him because he's trying to play devils advocate. Sil doesn't like some of the people we invited so now she's saying we're choosing them over her and making a huge fuss. FIL also lives in another state and she's demanding he come down for her birth and not mine. What in the actual shit. Why can't he come down for Christmas for the whole family to get together and BOTH our kids will be born. I'm about to block everyone forever and idk how to handle this at all. Does anyone think I should have went out of my way to make sure every person could come? Am I suppose to reschedule this to fit other people's needs. Idk how all this is suppose to work but I thought my bf and I called the shots on this and were about to just have the Effie cake alone and quietly have our first and fade into the shadow of sil.