There’s a lot of catastrophizing going on here.
OP is 69 and her husband 75. They are in good health. Their house is large and next to a golf club which would suggest that it’s in a desirable location. They have considered moving to a smaller place but not for the moment so as to accommodate visiting family. OP’s family tend to be long lived.
Wills can be changed or codicils added as circumstances change. Right now, I imagine he’s thinking that were he to die soon, a life tenancy could easily go on for 20 years or more. It isn’t unusual for a life tenant to outlive remaindermen. He would like his chlldren to inherit sooner rather than later.
This is a situation all couples who have had children from previous relationships need to consider when buying assets jointly.
A few years down the road, all kinds of circumstances may have changed so that one or both parties may wish to change the terms of their Wills.
Far too many issues over Wills are caused because people do not update them regularly to take into account their own changing circumstances and needs and those of their intended legatees.
Were this couple to reach age 80 and 86, they may well decide that respective life tenancies wouldn’t mean that adult children have to wait so very long for an inheritance. By then the couple may have moved to a smaller home anyway where both have the capacity to buy out the other’s share, which only he could do at the moment. As time goes on and they age, they may realise that the surviving spouse would find a(nother) move too onerous.
If the current two year stipulation is stressing OP excessively then perhaps a codicil to extend it to three would be a compromise.