Residency Exclusion for Capital Gains 2/5 years for triplex? Pror

[Will F.]

I own and live in one unit of a triplex (three houses sharing one lot).  I just wanted to confirm that I'm OK moving from unit to unit to still get the capital gains residency exemption:

Would it be OK to prorate the amount when sold of where I'm living % based on square footage of the units?

For instance I've lived in unit 1 for 2 years, then I move to unit 2 and live in for 2 years.  Then as long as within 4-5 years I would still get the capital gain residency exemption when I sell correct?

And I could prorate the 2 units based on square footage correct?  Or would I have to just prorate by unit amount like 2/3 of the total capital gains?