I'm sorry to hear you find yourself in this situation OP - it sounds very tricky.
I think in your shoes I would play a long game for now. Develop a strategy to put yourself in a stronger financial position going forward whilst you're still together - IF you think you can endure the current situation for a while. Make no mention of divorce for now.
Who controls the finances in the household? Your H has a much higher salary, but do you both have access to the family pot?
If so, I would start the following:
Open an online bank account in your name only, and a savings account known only to you. Build up an emergency fund.
If things turn very sour and you need to leave quickly, or the situation becomes untenable, you will have easy access to online banking facilities, and savings to tide you through an immediate or short term crisis. Never rely on a spouse to behave reasonably and fairly - they might but sadly they often don't!
Open a SIPP (self invested pension) in your name, and start making contributions from the family pot. You can contribute up to the level of your net annual income and receive the tax relief on top.
Pay down the mortgage as quickly as possible and any joint debts. It will give you a greater amount of equity to share out from the property when you split.
Make copies of all financial documents/ statements of income, savings, pensions, and other assets and keep these updated regularly.
Open and/or start topping up your DC's JISAs. This at least will be protected from any protracted financial negotiations in the future.
Increase your hours and income where possible, to build your credit rating and improve your own credit score. Ensure your income is not paid directly into a joint account, but move it over from a secondary account in your own name.
Research online resources on divorce. Book a session with a solicitor (online or by phone to keep costs down). Find out the likely outcome of financial agreements so you are forearmed with the knowledge you need.