Stalling isn't the answer. It will just become the elephant in the room and affect your relationship.
When a situation like this affects you personally it can be hard to not be emotional about it and feel hurt.
I can understand how he wouldn't want to be shafted in the event of a divorce, but he's not gone about this the right way really.
I hear all the comments about you giving up your career and being a SAHM, but you were able to do that as soon as you had kids, indicating that his wealth was accrued before meeting you.
You didnt play a part in his wealth at that point.
I think him protecting his assets prior to meeting you is fine.
From his perspective, he still works...your kids are in school and you could work more hours, but in the event of a split you become a lifelong expense to him...unless he does a clean break settlement. He would have to financially support you, because if married as your income is not enough to live on.
He might not mind doing that when the kids are still young, but when they're adults and he is still having to work for an Ex wife, you can see how he wouldn't be thrilled by that.
I'd be happy with a prenup giving me a very good set figure as a lump sum, child support, an agreement to pay/contribute a set % of university expenses for the DC, full ownership of the property you live in and bear in mind that you won't have had much in the way of NI contributions...so what about your pension.
Being old and poor isn't the best.