we haven't been consciously keeping our income low. Maximising income is an interesting concept.
It's not just not maximising income. There has been a deliberate lowering of it. By taking a pay cut and "protecting your CV". In the face of high additional costs in the form of fees. Costs that stand/stood to grow given that there are three children to get through compulsory education. And then uni ?
Sometimes we do stuff becuase we know what we don't want. But don't know how to make that happen. It's not always easy to say that we feel like we are drowning, and former priorities now feel like a concrete life jacket.
With your DH both "growing weary", having taken a pay cut and "protecting your CV" it might be worth asking yourself what extent he is possibly trying to create a superficially "by accident rather than design" set of circumstances that forces the issue and take spiralling fees off the table altogether.
Maybe sitting down, not to talk, but to really listen (and giving him an overt green light to put on the table what he feels is the cost/benefit of private schooling for the family on every level) might be a place to start before making any ".how can we swing this " plans ?
This might be redundant. Maybe when you talk about what you think/want/value/prioritise you mean both of you, now that he's had a chance to sleep on it. It's just... he doesn't get much of a mention in the way that you and the kids do. But the whole caboodle basically falls or stands based on his ability and willingness to keep on bringing in the salary needed to pay the increasing mortgage payments that are keep the education choices afloat for the time being.
IF (and it's an admittedly Very Big If, because it is almost impossible for outsiders to know what a 3rd party is thinking/feeling in this format, especially when there are only a few minor references to them), there is any chance he is feeling a bit "concrete life jacket" about your earlier education choices it really is worth getting it out in the open sooner rather than later. Because if there is any "flailing quietly under water" going on the whole family tends to get drenched in life rain when it abruptly stops being a secret due to self sabotage or the throwing in of towels when it all gets too much for any more pretence.