My mom grew up in a household where she was the oldest and her younger sister (5 years younger) had a lot of mental health issues and anxiety which caused a huge strain on the family.
To cut a king story short, all the focus was the on my mum’s sibling and my mum was just pushed to the side of it all. It was like she didn’t matter and she certainly didn’t feel like she mattered to her parents.
My mum is in her 60s now, has always had issues with attachment and relationship forming and she still has very strange relationships with her parents…..it’s almost like she reverts to being a hold near them and wanting them to view her as the ‘golden child’ because she never felt like that as a child.
There is still a very tense under current between her and her sibling too…it’s like a sense of resentment that my mum has, that her sibling ruined her childhood and a normal relationship with her parents.
I guess my point is that don’t underestimate the long term affect this may have on your son if he’s not made to feel as important as your DD.
You ask what child you would choose, and I would choose the 12 year old.
Your daughter is almost an adult and is able to hold down a job and manage herself perfectly well whilst there, so yes legally she may still be a ‘child’ she is not a child in the same way your 12 year old is.