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If the 401k was cashed out by the estate, then either the estate paid the tax (uncommon) or the estate must issue a K-1 to each heir and you report the K-1 on the heir's tax return.
If the IRA was rolled over into 3 beneficiary IRAs, then each beneficiary will get a 1099-R whenever they withdraw funds. The beneficiaries have 10 years to withdraw all the funds and close the account. Additionally, if the brother was older than his RMD beginning year when he died, then the beneficiaries must withdraw at least the amount of their RMD starting in 2025, using the single life expectancy table in the appendix of publication 590-B.
https://www.irs.gov/forms-pubs/about-publication-590-b
Additionally, if the brother was older than his RMD beginning year when he died, and did not withdraw his own RMD, then the heirs were required to withdraw that RMD (presumably, 1/3 each, although it does not have to be 1/3 each as long as the total is satisfied). If no one made a withdrawal, then all 3 beneficiaries need to follow the procedure for a missed RMD on their 2024 tax return (assuming he died in 2024, of course.)
https://ttlc.intuit.com/community/retirement/discussion/i-missed-taking-out-2024-rmd-distribution-wh...
