This is a great space for a large family visiting DC, especially if you are going to spend a lot of time in the city. This was a nice, big house in a quiet, working class neighborhood, with lots of room to park in the driveway. We had plenty of room to spread out, with bedrooms and bathrooms for everyone. We cooked breakfast and supper at the house every day and had everything we needed. There is a Giant grocery store less than a mile away (along with McDonalds, Starbucks, etc).
We used public transportation to visit the city. We bought unlimited passes for everyone. The SmarTrip app on your smartphone can be used in lieu of a metrocard.
We walked to Edsall and Montgomery to catch Bus 322 (Clockwise) at Stop 1145 for the Van Dorn station, then took the Blue line into town. It took about an hour from when the bus picked us up to when we got to the Mall.
On the way home, we took the Blue line to Van Dorn, then Bus 321 (Counterclockwise) from the station to Stop 1141 at Edsall and Montgomery. Getting home could take a little longer, since the bus only leaves the station every half hour or so.
You can find a map of the bus routes online (VRBO won't let me post the link here).
You can track the bus' location using Transit on Google Maps or text "FFX 1145" to 41411 to get the next bus' arrival time.