So since neither are your spouse they will more then likely need to complete a direct trustee-to-trustee transfer of inherited 401(k) funds into an inherited IRA, following rules similar inheriting an IRA. The IRS waives any early withdrawal penalties for owners of inherited IRAs so they can withdraw at any time They can also take a lump sum distribution, though they cannot then move the funds to an IRA.
The distributions would need to follow the 10-year rule requires that all assets in the inherited IRA must be fully withdrawn by the end of the 10th year following the original IRA owner's death.
If you have any post-tax, or Roth money in the 401(k) those withdrawals of contributions from an inherited Roth are tax free. Most withdrawals of earnings from an inherited Roth IRA account are also tax-free. However, withdrawals of earnings may be subject to income tax if the Roth account is less than 5-years old at the time of the withdrawal.
Thanks again for the question @monicap1
All the best,
Marc
Employee Tax Expert