Use of gendered language is marginalizing to nonbinary people.
It's easy to figure out why these changes are being made in particular, once you take a position of empathy.
References to brothers or sisters, or mothers or fathers, is offensive to nonbinary people? In all seriousness, not trying to start a flame war, why is that? Is a reference to hair offensive to a bald person?
The reason to replace an aggregate ‘brothers and sisters’ with ‘siblings’, ‘mothers and fathers’ with ‘parents’, or ‘boys and girls’ with ‘children’ is because for all of these the replacement suffices without calling attention to gender when it’s not necessary to do so.
There’s also an argument that the ‘X and Y’ phrasing makes the ‘X’ seem more important than the ‘Y’, or makes it seem like the ‘default’ - just a little, but with repetition the impression is reinforced. If there’s an alternative collective word to use, it avoids this ‘ordering’ issue with no real downside.
Note that all these arguments make sense in even if you consider gender to be a binary thing.
Regarding the first occurrence being conceived as more important, it’s the reason usually females appear named first, a sign of courtesy to them. That was sorted out neatly long ago.