The income from disaster distributions from both IRAs and pensions can be spread over 3 years. [Edit: I guess you sorted that out while I was typing my reply.]
I'm not sure I see a problem with the amounts on lines 5a and 5b. If what was reported on 2021 Form 1040 line 5b was the amount on line 5a plus the 1/3 of the 2020 disaster distribution from pension minus 2/3 of the 2021 disaster distributions from pensions, that seems correct. That should all be reflected on the 2021 Form 8915-F Part II. (Pensions in this context includes all non-IRA qualified retirement plans.)
Given the amount on line 5a, you apparently have other non-IRA retirement distributions that were not claimed to be disaster distributions.
