A former manager remarked to me one day that my one year old twins slept better than his 8 year old son. We've sleep trained all 3 of our children and I can't imagine our lives otherwise. I think we'd just manage to survive if they didn't sleep well and on their own.

This is my fear as well. Coworkers have mentioned similar where their wives co-sleep well into elementary school. I’ve met some of those kids, and they just don’t seem well adjusted — as in, during the day they don’t play by themselves unless a parent is nearby. My wife is in the same camp and just cannot bear our kids (1 and 3) crying, so it sabotages any attempt at training them to be independent at night. I finally had to banish her to a remote bedroom while I sleep train them.

I trained both of them at 1 and it only took a few days in a crib. The older one now has his own bed, so that’s been more challenging.

This is going to sound harsh but I think some bad habits like this are gotten rid of when their friend group finds out and makes fun of them for it.

We didn't sleep train our daughter - our organisation was pretty messy to be honest - and although she did sleep in another room from a reasonable age, sleep was incredibly patchy and broken for years. Which broke us too! Something clicked when she was around 7.5 years old, and her sleep has been pretty fine since then. I know you say yours is 9, but I write this to hopefully offer some solace that things do change, even if you don't feel like you didn't do the right things. (And which 12-year-old wants to sleep in their parents' bed?! So although it may feel a long way off, it won't last forever...)

9 is nothing, my daughter is 14 and still expects her mother to join her most nights.