Do the math and trust the numbers. Dont try duge any of the numbers just so you can make it cash flow on paper. Do your due diligence in checking both the condition of the property and the history of the tenants and expenses. Good luck!!
A few things to keep in mind:
1) the duplex/triplex vs. The property with the office will fall under different loan terms. Due to the office property being zoned as commercial . ( be prepared for a larger down pmt )
2) make sure you run the numbers on the properties so that you know you cash flow in advance (use the analysis calculator on this site... great tool)