I went to private school for more years than my brother and sister did.
I left with 4 poxy O levels, two of which were unimpressive DS and RE.
My brother got a couple of CSEs.
My little sister, who spent not a single day in a private school has a PhD in a hard science.
The most overwhelmingly important factor in terms of outcome was not the schools we went to. It was the stage we were at when my parents' marriage collapsed. On the second day of my O levels to be precise.
My ears pricked up at the albeit small and innocuous sounding mentions of your husband. Might be something, might be nothing. But the two of you don't sound on the same page. And as a family appear to building huge time and debt pressures that generally don't do wonders for the glue that holds a couple together.
I'd take a long, hard look and assess the extent to which as pair the current situation might be wearing down, or has the potential to wear down the bonds between you in the future. Becuase a move as your daughter goes into year 10, while imperfect as a solution, is a million times better than leaving a pot to boil dry till it explodes off the hob in a year or two's time.
And you do sound under a horrendous amount of strain.
We all screw up. You might both have made wrong choices along the way. But the real measure of us is how we rectify those mistakes. So I think you both need to forgive yourselves and find way out of this that takes this awful, growing pressure off your family.