Having a goal to be mortgage free by 55 is a good one.
DH and I achieved that by 43 (but full disclosure on a much higher joint income, but possibly much bigger mortgage as well).
Having said that, it's not a straight journey from A to Z.
When the children were babies/toddlers we took a huge step back.
Cost of nursery/maternity leave (for me only 3 months then part time) etc couldn't be ignored.
We cut back stopped on savings/mortgage overpayment realising that (unless we sent DC to public school) this was the time our income would be stretched the most.
Children grew up...
After school clubs were a third of the price as nursery. So being used to our low disposable income we threw the difference into savings and so on.
Got the DC all to great school's and then started to "claw back" and did some property upscaling increasing equity and plus overpayments, zapped the mortgage.
Right now, you're in the worst place financially so so something has to give.
Your DH's aspirations might be set back, but it's perfectly possible to get back on that track should you both wish to.
What won't be resolved is the anxiety of wondering how you pay for nappies right now and you'll feel the repercussions (rather resentment) of that for years.
My advice is (like a pp) cut your pension contributions for a few years (only a few years though) and get an interest only mortgage (again for a few years).
Right now you need income to "buy" future security.
Disposable nappies (whilst great/environmentally friendly/cheaper/very much recommend) are not the solution to the wider issue.