ILR calculations for partner

i landed in uk June 2019
my partner landed in uk october 2019
his BRP will expire in september 2022 (since i landed before him and it seems dependents BRPs are in sync with the main applicant BRP)
I plan to apply for my extension when my BRP expries september 2022
if i get the extension for 2 years:
the new BRP will expire september 2024
if i apply for ILR right after the end of extension, my partner would not have had the 5 years accumulated (short by 1month)
the Tier 1 program will end in april 2025 and no extension is allowed after that.
what would be the options for me:
-do another extension for me (will this be possibile since program will end in april 2025?)
-do an extension for my partner for 2months (is this possibile?)
thanks for any help on this in advance

When was their visa issued?? ILR counts from visa issue date not date of arrival in the UK.

Your extension brp will expire 2 years from date of approval. If the application take a few months, the date of visa start is the date of approval, it is not tagged onto the expiry of the last visa.