Because your father will retire in 2022, 2022 becomes his first RMD year. Because he will be subject to RMDs for 2022, he is not permitted to do any rollovers from the 401(k) until he satisfies his 2022 RMD from the 401(k) accounts. If he wants to postpone 401(k) RMDs until 2023, he can't do the rollover from the 401(k) until 2023. That includes the Roth 401(k) because Roth 401(k)s are subject to RMDs. If he waits until 2023 to do the rollovers so that he doesn't have to take the 2022 RMD in 2022, he'll have to take the 2022 and 2023 RMDs from both the traditional 401(k) and Roth 401(k) accounts before rolling over the remainder.
He'll want to evaluate if it makes sense to take the 2022 Roth 401(k) RMD in 2022 and roll over the Roth 401(k) to a Roth IRA in 2022 so that he will have no 2023 RMD from a Roth account. He'll generally want to do a split rollover of the traditional 401(k) with the after-tax portion rolling over to a Roth IRA and the pre-tax portion rolling over to a traditional IRA. He might want to evaluate whether it makes sense to take the RMD for the traditional 401(k) in 2022 and do the split rollover of that account in 2022 so that there is more after-tax money that makes it to the Roth IRA than would be the case if he did the split rollover in 2023 after taking the 2023 RMD.
