How do i know who us savings bond interest belongs to?

Husband cashed US savings bonds that stopped earning interest in 2015.  Bonds say "Gift" and SS# that must be the purchaser's. Then, son's name "OR"  and then husband's name. Received 1099 w/ husband's SS # . How know if the interest  belongs to son, my husband, or half to each of them? If some or all should belong to our son, how do we fix it?