Repeating what I said earlier:
You must complete his 2023 RMD for the traditional IRA. The deadline to complete his 2023 is December 31, 2023, but you get an automatic waiver of the excess accumulation penalty if you complete it after 2023 but by the due date, including extensions, of your 2023 tax return.
Regarding beneficiary RMDs from the inherited traditional IRA, your first beneficiary RMD is for 2024. The deadline to complete that RMD is December 31, 2024.
Regarding the Roth IRA, it usually makes sense to treat the inherited IRA as your own so that you will not have any RMDs. If you instead choose to treat it as an inherited Roth IRA so that you have tax-free access to earnings before age 59½, you would have annual RMDs as an eligible designated beneficiary.
You can assume ownership up until the year you reach age 75. (The proposed rules say age 72, but those were written before the SECURE 2.0 Act changed the beginning RMD age, in your case, to age 75.) After that you can move the funds to your own IRA by distribution and rollover, subject to the one-rollover-per-12-months limitation. There is no reason not to assume ownership once you reach age 59½ because the only reason to maintain the account as inherited is to have penalty-free access to taxable amounts and the 10% early-distribution penalty disappears from your owned IRAs once you reach age 59½. Seep proposed regulation 1.408-8(c):
https://www.federalregister.gov/documents/2022/02/24/2022-02522/required-minimum-distributions
