So I went ahead with the upgrade opton (which incidentally was showing on the mobile but not on the web version LOL) and proceeded with the 3 upgrades of one leg for the amount shown.

I called them up to ask if they would split the upgrade in the passengers but they said they couldn't

The only question I have left in my mind is - did I pay more than I should have - as in - would the offer price have come down closer to the flight or it usually stays the same T-3 days to the flight till T0.