Hello

My wife and I are very happily married in our mid-fifties.
We each have children from our first marriages, all over 21.

At present we have mirror wills leaving everything to the other unless
the other is dead or dies within 28 days in which case it is shared
equally between the children with any already deceased childs share
split equally between their children.

It is not inconceivable that one of us might survive the other by 30 or
40 years and possible marry again.

How can we ensure that the interests of the children of the first
deceased are protected? We have no reason to distrust each other but
anything could happen in the possible timescale available.
Total net assets are around GBP400K including a house worth about GBP350K.

Just trying to get some ideas before taking advice.

TIA for any advice.