@Sergio Santos
There are no issues with renting out rooms to separate tenants in Arlington. Not sure about the condition of your parents home, but if they've owned it awhile and don't have a mortgage, if it is the typical, older Arlington home (small, not renovated, original sewer and plumbing pipes from the 1930s and 40s), you might actually do the math on tearing down the old house and building a new single family home in its place. Once that's up, sell in the $1.2 million+ range and potentially pocket several hundred grand. Rinse and repeat!
There is a reason why most developers are doing this in Arlington with older homes in prime locations, as that's where the money is. The people who are making money off of rentals in Arlington have owned their homes a long time and bought when homes were a fraction of the price they are now. These people don't want the cash, but a steady, stable income.
I personally have rentals in Arlington not for the rental cash flow, but for the appreciation and the quality of the tenants there. If I was in your situation, I'd probably do a tear down, new build, then take the proceeds and buy more homes with that, maybe even a multifamily building if you can swing it.