https://www.irs.gov/pub/irs-pdf/p970.pdf
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Changing the Designated Beneficiary
There are no income tax consequences if the designated beneficiary of an account is changed to a member of the beneficiary's family.
Members of the beneficiary's family. For these purposes, the beneficiary's family includes the beneficiary's spouse and the following other relatives of the beneficiary.
1. Son, daughter, stepchild, foster child, adopted child, or a descendant of any of them.
2. Brother, sister, half brother, half sister, stepbrother, or stepsister.
3. Father or mother or ancestor of either.
4. Stepfather or stepmother.
5. Son or daughter of a brother, sister, half brother, or half sister.
6. Brother or sister of father or mother.
7. Son-in-law, daughter-in-law, father-in-law,
mother-in-law, brother-in-law, or sister-in-law.
8. The spouse of any individual listed above.
9. First cousin