No Contingent Beneficiaries

If you leave your home to two adults, who both have two kids, and one of the adults predeceases you, the house goes 100% to the surviving adult beneficiary (this is also how many beneficiary forms for  financial accounts work).  

If both adults predecease you and you do not file another transfer on death deed, the house will go through probate to your next of kin unless you have a will or trust that says the house will go to someone else.  

A trust will allow you to select different contingent beneficiaries, and the house does not go through probate.  This allows for the distribution plan that most people want - i.e. it goes to my child, and if she is deceased, to her kids. If anyone entitled to the house or to funds from the sale is under 30, those assets are managed in trust by a trusted adult who serve as trustee.