Not especially closely.
Interestingly, none of them have sisters, whilst I have a brother and two sisters.
They're all educated and professional high achievers.
Two were only children.
One told me she had a "sister fantasy" as a child where her long-lost sister showed up and they were best friends. She's taken her older daughter on numerous solo trips abroad since she was a toddler, and says she'll do it with her son at some point - but the years roll on and there's no sign of it.
One of the others has a dysfunctional relationship with her own mum, seeing her as preferring her brother. But to her credit, whilst she's happy to have a girl, she is appalled by how the other woman treats her son.
The last had difficulties with conceiving, so whilst she does want both ideally, I can see that she knows that she may only have one child, which she has a preference for one sex (she was also only pregnant, so at the stage where your imagination has more power than the actuality of the person you've made).
As for MIL, that side of the family endlessly spouted sexist bs about both sexes. My family just saw him as another baby, a blank state.
So overall, I don't generally hold their opinions in high regard.
However I've had other friends express preferences for girls openly, in front of me who is happy with one boy, and another friend who'd love to but can't have another child of either sex.
And at work, it was incredibly depressing to have a string of older women telling me that girls and women were awful and I was better of with a boy.
(As it happens, my son is widely accepted as the most cheerful and delightful little soul amongst his contemporaries - all the other parents of boys or girls tease me that I've got off fucking lightly as a toddler mum, and I know it.)