If one of you dies, his parents get the house. Unless you have a will made naming you next of kin. His parents will also be beneficiaries on insurance and pension (along with the children) unless he has specifically named you.
Given that he has children, surely they will inherit, unless he specifically has a Will naming his parents? Why would his parents inherit anything when he has children? I am not legal but his children would inherit everything, surely.
So his portion of house would go to children, Ops portion would be hers.
His parents might want their money back, but unless they have anything legal to show they are owed a % of house, they wouldn’t have a right to anything in law. Not sure how Pre nup would be treated if he died? Does it die with him? But even so, it applies to him getting the deposit money, not his parents!
Similarly with pensions and insurance, even without him naming anyone, the trustees would consider paying out to his dependants eg children, first, not parents. Op may have a case for insurance as she is bringing up his children. His parents would be further down the pecking order.