The 4 unit is grand fathered in and all 4 units are legal units.  

couple grand well that's not a big issue

Expect a couple grand, maybe 3 grand total if it gets to a hearing, but it probably won't. 

Does anyone know of a such company in Arlington, Grand Prairie area? 

You can snag Medical/Dental/Law/Pharmacy Students, or some of the new Fellows through various foundations who trying to score a cheap place, $400-$600, in the City(requirement to their employment) but don't have the money to live in Downtown, Midtown, Lafayette Park where one bedrooms start at $1000/month, two bedrooms start at $1300.Check areas off/on of West Grand Blvd, but south of Michigan Ave.Also,Right now The North End is in play, thats the area off of Woodward but south of Highland Park.

We even find some with simple value-add plays (like adding an extra bedroom for a few grand) in that price range.Using your ROI metric for 6%+, it shouldn't be an issue.

But as @Darwin Crawford said there are FAR more options for investing in the Phoenix Metro Area and way more demand.If want something a little more rural but closer the metro, try Casa Grande.

You can let Grand ma live in it for free. 

I now have an opportunity to acquire few new homes 3B 2B 1G in South east of Silver spring shores and also Belleview and Summerfield areas for 160ish grand range.I would like to know from fellow Central FL investors how do these areas compare?

I've had good luck with a company called Foremost based out of Grand Rapids, MI. 2) Definitely get an STR specific coverage.