Inheritance really is different, and not just a lump sum to go into joint finances - no matter how long you've been married.
It's a continuation of the people you loved, and can be felt as them continuing to take care of you after their death. It's also their legacy - the product of a lifetime of work and care - which you want to respect and protect.
Having said that, running that legacy down by retiring at 55 doesn't seem entirely sensible if you're not fully financially secure, which to me includes supporting DC through university and some help with house deposits, as well as your own pensions.
There's also the question of maximising the benefit he gets from it. Instead of just using up the money, he'd get much more benefit if he kept working for a few years and put the max into his pension (potentially yours too if he's willing/there's too much to go into his pension in time/you're a higher rate tax payer). Then he can benefit from a 20% uplift on his inheritance (through the tax free lump sum) as well as making use of the £12.5k annual personal allowance until SPA. It's financially very effective, even as basic rate tax payers. (Just be sure to keep his taxed income above the personal tax allowance!)
At 55, he's allowed to take it back out of his pension at any point, so he'll have access to it once he's had enough.
The other thing to consider is that since you have pre-Uni children, you could take advantage of the statutory right to unpaid time off for children under 18. By law, you're each allowed up to 18 weeks per child before the child's 18th birthday, with a maximum of 4 weeks per child per year. You could both stay at your current jobs, but take extended unpaid breaks over the summer and enjoy some incredible family travels before your children leave home.
But be gentle. In the end it truly is - and should be - his choice.