Why not just continue to rent out your house, as you do now, to provide you with an income. If you die first, your house goes to your family-no hassle. If he dies first, his house goes to his children (or just his wife's share, if he wants you to have half) and you move back into your old house or sell your old house then to buy out his family's share.
Why complicate the matter of buying a stake in his home now! What if, in the future, something happened and you divorced. You may think it unlikely but you never know. Or, what if one of his family wanted to live with you if their circumstances changed and it didn't work out too well for you. If it was me, I would keep my finances separate to ensure my children inherited all my previous wealth and I would just contribute a fair amount to your husband's household expenses.