I've been exactly where you are, OP. My kids are older now but DH has been a partner for nearly 2 decades, while I have also worked (also FT in a responsible role but without such crazy hours) and generally had 100% responsibility for children + home. What worked for us-
1 Complete openness about finances, all decisions taken jointly. It is madness that you are about to burn out while he is focused on investments. Investing can wait. There can be an attitude among lawyers that you inevitably have a fairly short shelf life and therefore have to plan on retiring early 50s at the latest, because no one can work at that pace forever, and that can mean investing a good amount an an early stage, but like everything it is a question of balance.
2 We have always had a cleaner (even when I was on mat leave) and paid for additional help as needed.
3 Understanding from DH that his career comes with burdens to you both as well as benefits. It's well paid but it's also incredibly disruptive of family life (DH is now super senior but still had to get out of bed at 11.30pm last night to do an hour long call 😭)
4 I think some of the comments on this thread are unrealistic- especially those about women not doing hours like this. In this sort of job, everyone does these hours and if you don't like it, you go elsewhere. It's unlikely that it's open to him just to work less. It is open to him to go elsewhere, however, for a bit less money and a more normal life. Whether that's a better course is a decision that you should discuss together.