Converting a single family into duplex

[A G.]

Hello All -

I am looking at a SF home that's current zoned as RML (which is low density multi family). The home is currently setup in such a way that upper and lower (basement) units each have 3/1 and 2/1 with basement have plumbing for kitchen. 

I am wondering if anybody can share their experience on how to go about evaluating feasibility of having a legal duplex.

thanks