default beneficiary is a catch all

It is better to have only one default beneficiary.  The use of default beneficiary is mainly to catch properties not mentioned by the will.

Let's say your will mentioned 1 primary residence and three bank accounts, and assigned those properties to multiple people.  But after your death they found out you had a forgotten account not mentioned by the will.  That forgotten account would go to the default beneficiary, i.e. catch-all. 

So it is better to have only one person serving as catch all.  If you have multiple persons as default, and if there is an forgotten property goes to the multiple default beneficiaries, there will be dispute as to how to divide it.