Also just because mom had a mental breakdown it doesn't mean she wasn't at fault as well. After all the reason she had it in the first place was the stress from Mogu not wanting to conform to 1 gender and insisting they're neither, which I assume she was just as much against as Mogu's father. If she was ok with it, she wouldn't break over it.
I would like to point out, tho, that I believe that their mother might've been pushed by their father as well. By the way he reacted to Sakura suggested Mogu coming back, it's highly possible the last days they lived with them were a living hell, and that might've caused the breakdown.
I'm not saying she might be completely out of fault, but maybe she would've been able to eventually be ok with Mogu's gender if she had had the chance to go through the process without him.
