This distribution cannot be rolled over to an inherited IRA. A 401(k) is permitted to be rolled over to an inherited IRA only for the benefit of an individual who is a designated beneficiary. An estate is not an individual and therefore cannot be a designated beneficiary. A 401(k) which has no designated beneficiary can only be distributed as income to the estate (code 4 on the Form 1099-R), not rolled over to an inherited IRA for the benefit of the estate (codes 4 and G on the Form 1099-R) or anyone else (although PLRs have allowed a surviving spouse to roll over to their own IRA under certain circumstances). Since the distribution was to the estate of the deceased, you must request that the payer issue a corrected Form 1099-R showing taxable amount in box 2a and showing only code 4 in box 7.
You should contact the probate lawyer and inform him or her of the error in attempting to set up an inherited IRA to receive this distribution.
Once the correct taxable amount shown in box 2a of a code 4 the Form 1099-R, see the following answer by tagteam describing how to report a distribution to the estate as Other Income on Form 1041 and possibly passed through as Distributable Net Income to the estate beneficiaries on Schedules K-1:
https://ttlc.intuit.com/replies/4549116
