We all want our respective families to benefit from our deaths especially if we have no children to which to leave our estate.
Take Rosie and Jim, a typical couple, living together not married, no children, want each other to benefit. Jim dies, in his Will he states that his estate is to pass to Rosie, subject to her surviving him for 30 days; Rosie survives Jim by 30 days and takes Jims estate absolutely, when Rosie dies both her and Jim's estates pass according to her Will, to her parents or brothers and sisters leaving Jims family nothing. This is possibly not what Jim would have wanted had it been explained to them both when giving their instructions.
So what are the options?
Option 1 is for each to leave their estate on a life interest trust for each other, and when the survivor dies, the trustees of the trust fund distribute the fund according to the wishes of the testator. However, trusts can be expensive and may also run for many years.
Option 2 is a cheaper alternative is to write the Will as follows:
I give my estate to my partner Rosie subject to her surviving me by thirty days and on her death the residuary estate to be held in two equal shares and distributed as follows:
One share to be divided between the family [named] of Rosie and in equal shares if more than one.
One share [or the remaining share] to be divided between the family [named] of Jim and in equal shares if more than one.
Failure to take account of both families can result in a negligence claim from the aggrieved beneficiaries. Although we have used an unmarried couple, it does not matter whether they are married or not, the result is the same.