If land is at a discount there may likely be extensive sitework costs - if you purchase an existing complex in a good location your improvements will increase rents/value with the opportunity for conventional financing. 

Feel free to reach out if you have any tips or info to share.

My family would like our grandparents home built in 1964 fully renovated and upgraded.

They were in model home condition. 

My brother and I purchased a home 18 months ago in which the seller wrote us a fixed 4.5%, 5-year mortgage note as an incentive for a quick closing.

split the home into two units, upgrade appliances, add hvac, split the yard for each unit.

I want to offer me purchasing their home  but I dont want to go the bank route because I can't afford to put a downpayment more than 50k & have a mortgage of 7k.  

Granted MFH are more common in rougher parts of central jersey and my purchasing power can't acquire me something in North Jersey here homes are much more desirable when it comes to appreciation and schools and safety.

Nightmare story,I've bought many homes before but this was by far the worst ever. 

If you know that going into the deal, you will know to offer a little less on the home.