(I had grading done in Michigan for $1.5k along one outside wall, which solved my problem.)BUT, if there is a serious horizontal crack in the foundation, that could be an expensive repair ($10k at the low end).

Are they in good shape and not cracking/peeling? 

The inspector recommended I get a licensed HVAC engineer to check it.Other things are ---Open mortar joists/loose spalled brick at the chimney, loose shingles on dormer---Several windows painted shut sash cords missing, non-operable, rear deadbolt "keyed only" should have thumb turn for emergency egressloose/ flaking paint, possible lead-based paint---Cracked concrete at entry porch,--missing guard rail at rear steps,--several downspouts missing splash blocks/draining too close to the house---Grading is flat to sloping toward foundation additional top soil/grade modification may be needed---Suggested GFCI protected outlets at all wet locations as a safety improvement---Discoloration on floor joists in the basement, have evaluated for cleaning, possible treatment---Garage needs to be repaired completely.

Over the phone the said 3.5 but I got my paperwork back this morning and it's up a tiny bit.

The duplex was built in 1940 and has had some foundational cracking (though there is nothing on the interior to indicate any structural issues), in addition to some overhanging porch and possible roof repairs that need to be done in the near future. 

You may pay a tiny bit more interest in the end but is worth having the control.You should think about what your plans are with investing and long term goals.

Me and a friend have land near a lake and want to put a 2-4 tiny houses out there for people to rent out via Airbnb.

A lot of people are flocking to STR in Gatlinburg area right now as well as there is high cashflow there if you get a good price, as well as a STR market that nearly all feel will continue being STR friendly, as opposed to some cities cracking down on them - check out BP podcast 364 if you have any interest in this.   

Stop buying tiny properties with the hopes of pulling cashout in <1 year.6.

I love it when I hear someone is investing in big multi-family or in building a tiny home community or self storage.