I'm trying so hard not to crash out for my sister but I need advice on what to tell her and what she should do.

To start, my sister is giving birth a earlier than anticipated because of pregnancy complications. She had cancer growing up and did chemo and now its affecting her pregnancy, hence early delivery by c-section. Her and her bf toured the hospital she was gonna give birth at and looking at the size of the delivery room, only 2 people were gonna be able to be in the room with my sister. Anyways so recently, we celebrated her baby shower and it was a little bit of a mess. My camera broke to take pictures for her, the games were fun but chaotic, signs kept falling off the wall, and her bf's mom was being rude to our mom. As I was gone to BB to buy a new lens, my SIL told me that while they were serving food, his mom pushed my mom to the side because "she wasnt helping" when she was trying to help... my SIL noticed it and my mom let it go bc she wasnt about to fight on an important day. 2 mins later, his mom complains that she isnt helping...bruh. anyways fast foward to now, his mom keeps begging to let her be in the delivery room. my sis chose our mom and her bf to be in the room. his mom says its "unfair" and "disrespectful" for her to not be in the room. my sis has told her MANY times that she doesnt feel comfortable with her being in the room, it wouldnt be fair to kick our mom just for her to be there, and that she should support her reason. she also told her after the baby comes, she wants ONE day to themselves to relax and then everyone can come and her the baby. his mom starts yapping about how my sis is trying to "exclude her" and how "unfair" is it because its her first grandchild. its ALSO the first baby/grandchild in our family.. we dont act anything like her. my sis sent her a message saying she needs to calm down and support her during this stressful time and the decision was hers to make. his mom says "okay" and then starts crashing out on facebook. she started posting indirect quotes at her and removed her from his moms fb pic. very childish and immature IMO!! his sis is calling my sis talking about she isnt being fair and that shes manipulating him to not letting them be in the delivery room or to even see her. and then his mom also brought up his ex and it made him pissed. this whole time, hes been scared to say something to his mom (as he is the only boy in the fam) and now that is ex is brought up, theyre gonna talk to his fam this weekend.

what do you guys think? any advice? hope they dont see this lol