If the refund is from a return filed before your mom passed, then it's technically IRD since she would have received the refund (and interest) had she survived.
As a result, the interest would be income to whoever receives it. Since, apparently, that would be you at this point, @jlr00721, you can simply report it on your 1040 and indicate part of the interest was received as nominee for the other three beneficiaries (and then issue 1099s to them along with their share of the interest).
Alternatively, you could handle this scenario as @NCperson set forth; as a gift to the other three beneficiaries less any tax liability you actually paid after reporting the entire amount of interest on your return. The amount would be well under the annual exclusion so that should not be an issue.
