division of equity %???

It sounds like you are talking about a Mesher Order by which when the youngest child is 18 your ex will be entitled to a percentage share of the equity.

This is possibly a good option in the circumstances, although will your ex agree?
As for percentage yes you can try and trade off pension to acquire a larger share of equity although it sounds like your stbx may not not be willing to agree this?

Another thought is that you possibly should try and negiotiate some Spousal maintenance if he earns 5X more than you. Its worth doing some costings to see how short you would be each month if you took on the mortgage.

That sounds like a Mesher Order. You live in the house until certain triggers (eg you re-marry) or the children reach a cetain age. Usually its when the youngest reaches 18.

The problem is your stbx would need to stay on the mortgage as the lender is unlikely to let it be in your sole name. This would mean he would be unlikely to be able to get another mortgage for 10 years. Would he be likely to agree this? You would also need to be able to demonstrate that you could afford to make the mortgage repayments and run the house on your own during this time with your income plus whatever benefits and maintenance you will get.