I am seeking applicable first steps as to how to turn my primary residence SFH into a Co-living space. 

Alternatively, instead of lowering credit score criteria you can give them an opportunity to apply with a co-signer - but again, you have to apply whatever your rule is to everyone equally.

First, I wanted to buy an apartment in a Co-op or Condo in the city BUT the HOA alone goes between $2,5k and $3k plus mortgage monthly so that was a big NO.

I was wondering if it is legal to have a sibling do a mortgage application with me and my wife as a "co-borrower"  as a primary resident and use that to our advantage for lower rates and down payments for a rental.

Hopefully you have a CO detector with 5 ft of the chimney venting.The last chimney a friend took down was $8k in removal & dump fees & he went direct vent.

@Zander Dragony@Wayne BrooksFor FHA;A SFR - A family member can be a co-signer and you still do the low down payment option.A MFR - All co-signers regardless of the relationship requires 25% down payment. * Also note - a MFR you can use 75% of the rental income from the other units to help qualify for the loan.

We joined a co-op here in Orlando and after evaluating the cost as well as what value it would add to our home we decided to pass.

I am now trying to get into a fourplex which my mother will occupy - she will be in the title and I will be a co-borrower on the mortgage.

It's not only about credit score and down payment, they are assessing your ongoing ability to pay given your other required payments.It could be perfectly reasonable if you hack it with some roommates, duplex maybe, and/or get a co-signer. 

possible to  line up a  co borrower  ?