The thing is, C isn't the one that is insisting on a date change...and C is really the only one with a conflict. K's parents are being ridiculous at best and if I were C, I'd be scared to death and how involved and present they plan on being during and immediately after the birth of my baby. Heck, C may even want them to be distracted by K's wedding.
I don't think K was rude not to consult with her family members before choosing a date. She's obviously not springing this on them at the last minute (she's at least 6 months out, right?). She chose a date that was important to her and her FH and then told her family the date. If she's expected to find an ideal time for her immediate family, her FH's immediate family...then where does it end. She can't forget about her best friends, grandparents, Aunt Ethel who's always been there for her, etc.
This is her special day and if it's important to her friends and family, they can start making arrangements and fixing their schedules so they can be there...and if they can't, that's ok too. But it's pretty awful, IMO, for anyone to say "Change your wedding date to accommodate me."
And I'm trying to picture how this conversation with C was supposed to go. "C, I know you are trying to get pregnant. How's that going? I'm planning my wedding and I need there not to be any conflicts. What date works for you?"
"Well K, thanks for asking. Not pregnant yet, but I'm going to keep trying so can you hold off until I'm successful and then plan for something a good 6 to 9 months later to make sure that everything is fine with the baby and I'll be up for going."
It just doesn't seem to work. Since K and C are already discussing ways for C to see the ceremony, then I think that K is in the clear. She knows her sister cares and wants to be part of it in any way she can. If I were K, that would mean as much to me as her attending.
If only we could say her parents (who have zero conflict) are being that reasonable.
I guess that perspective is based on family dynamics. In my family it would be perfectly reasonable to expect the mom and grandfather to be at the hospital when the baby is born and to be available to help out when the baby comes home.
If that is the case in this family, the mom is going to spend the next 6-7 months hoping that the baby doesn't come until after the wedding. I know I'd feel aweful if I had to tell my DD who had just delivered a child "Sorry, sweetie, I've got to leave now to go to your sister's wedding." While I'm sure my DD would understand, it would still be hard to do. Or worse for them to get a call during the ceremony that the baby been delivered, but the grandparents can't leave because they are at a wedding or if they did leave, they'd feel like they were abadoning one DD for the other.
That's just additional worry and stress I'd never had wanted to put my mom through. And my mom would have stressed about it. She never wanted one of us to feel less loved then another so trying to balance to things like this would have drove her a little bonkers.
It's customary in my family as well. But that doesn't mean the family is on lockdown during that time either. Like I said earlier, I'm sure it would be a lot for the parents to both help their older daughter prepare for her wedding and their younger daughter to prepare for a baby, but it's not impossible. If C was really expecting that her parents be there 24/7 during and after the birth, she's being unreasonable....yet, she doesn't seem to be the one that even cares. So it seems to me this is more about the parents putting importance on one event and stating that it trumps all others. It doesn't. As a matter of fact the wedding date is a known, so C can already be certain that the day of the wedding and possibly even the day before, her parents will be attending to her sister. If she hasn't had the baby yet, then great. And if she has, then she knows her and her DH are either on their own or will rely on help from his family or friends that aren't at the wedding.
The only possible conflict I can see is if she happens to be in labor the day of the wedding, but again...what is the grandparents role? Sure it's nice to have them there waiting in the lobby or even holding her hand during delivery, but it's not necessary. Again, I think that anyone who thinks that everyone else has to be there 100% for them to help them care for/celebrate a new baby is unreasonable.
And why would a parent feel awful for leaving a daughter alone to care for and bond with her new baby for a few hours but not awful in missing her own daughter's wedding? If I had two daughters (or two children), as a parent, I would never minimize a life event of one in favor of the other (I hope). I think a better reaction from her parents would have been "Wow! What great news! A marriage and a baby the same week. I'm so excited for both of you and happy to help you in any way that I can. I'm sure we'll all be exhausted that week from all the big changes, but what a good exhausted."
Really, the only consideration that K and C should make for each other at this point is to be sure not to schedule baby and wedding showers on the same day.
ETA: I think that the mom can stress about it all she wants. I know I would love to be in the room (or just outside it) the day my first grandchild arrives, but to expect my other children to rearrange their lives to save me from worrying about something like that is selfish. For the bolded, I think asking/expecting a daughter to move a wedding date so that I could be available 'just in case' my other daughter has a baby that day, is making it look like I love one more than the other. Is it really sending a message of "non-love" to attend a daughter's wedding and then go to the hospital after to coo over my hours old grandchild? Is that few hours really going to hurt my relationship
with my other daughter or even the grandchild? If so, they are the ones that are being unreasonable, not the one who didn't postpone her wedding for 6 months.
And FWIW, my younger sister was 4 or 5 months pregnant with her second child during my wedding. We actually had to get her a new dress at the last minute because the one we had for her didn't fit. She also had some complications that caused us to have her sit vs stand during the ceremony (she was in the bridal party). She wasn't pregnant when we announced the wedding (but I also didn't consult her first). And if I had waited for her to stop having babies before I got married (she had them every 18 months to 2 years apart and pretty much in the 'trying' stage the whole time), instead of getting married 13 years ago, I would have gotten married 6 years ago.
And when I was pregnant, we planned for my whole family to be there for the birth. Instead, we delivered 6 weeks early. My parents were in another country on vacation, my brother wasn't due to arrive in town for another 6 weeks, and my sister was at some event for one of her children. Life happens...and not always how we plan.