How can I add more units to my triplex?

[Peter Ngu]

Hey! Thanks for stopping here! Heres the back story:

My Triplex had fire damaged that was caused by the neighbor house

The First floor has 1 unit and 1 illegal unit. (city is making us remove the illegal unit). Picture below shows a purposed ADU my architect drafted up.

The Second floor has 2 units. 

And the Third third Floor has a huge space and i want to ask y'all if i can even convert it to another unit?  

The building is 3710 SQFT on a 6437 sqft lot in Oakland, CA

TLDR: If the Property is a triplex how can i get it to a legal 5 units? or is it not possible.