Thank you for using justanswer. First, congratulations on the birth of your daughter! What a wonderful gift you received this year!
If I'm reading you correctly, you live in DC and your husband has his "home of record" as being DC, but he works in MD, so I'm assuming that he filed and paid taxes as a non resident of MD.
If the above is correct, then you pay capital gains tax to the state that you consider to be your home state, which sounds like its DC from the information above.
In order to meet criteria to exclude up to the full $250,000, you and your husband must BOTH meet the "use" test (meaning you both used the residence as your main home for at least 2 out of the prior 5 years before the date of sale.) Please see below:Excluding the Gain
So, unless your husband has lived in the DC home for at least 2 years, then you will want to continue to file jointly with DC being your home state, and your husband filing and paying taxes to MD as a non resident .
I hope this helps.