Also, make sure you lay out the specifics of the partnership so the roles and responsibilities are clear and please use a formal agreement. 3.

Perhaps the ideal layout to maximize the lot would be something like this image:My question is:  can I build 2 duplex's, one on each side facing the street ?

I know it sounds counter intuitive, but you can increase your passive income by claiming everything legally possible as capital expenses. 

I have two options in front of me either to obtain a rehab loan, which will cost me $10k for six months ( points, fees, interest) or just finance the entire deal with my own money (cash).The rehab loan will enable me to obtain an additional property, so in six months i'll have two properties ( one with the loan, another with my cash)  but it'll cost me an extra $10k (on top of the regular down-payment which in any case i'll have to lay out) .

The layout is apartment style,  but they call it a condo.

Also the layouts, are they true 2-bedrooms or is a "bonus space" counting as a 2nd bedroom that almost nobody would use as such? 

After starting the project, the architect and OCD in me took over and I ended up changing the entire layout of the entire house and we went way over budget on electrical and plumbing because it was the right thing to do with the condition of things.

I have a identical fireplace lay out in my home, wall to wall, raised hearth  (much nicer brick) and have not used it in 25 years.

It may sound counter intuitive but if you can find an investor locally who is willing to let you split the cost of investing and split the cost of the profits you are far better off.

Depending on the layout of the apartment, you might be able to get away with fewer.