Mine to keep?
Pay off mortgage
Decorate and extend
That would use half.
£50k each for the DC for the future so invested for now (and because we no longer have a mortgage payment I'd increase the amount we save monthly into their pensions).
£50k to buy a buy to let (which I'd let at bargain price to a woman escaping domestic abuse) obviously that wouldn't buy it outright but would be a decent chunk on a mortgage for a buy to let. I'd follow all the rules in Scotland and more. Would aim to be a "good landlord". Would work with local Women's Aid to set the home up and ask them to suggest women to live there. I have relevant links to this area.
£50k to help sister in law
£50k emergency fund