On the day after Christmas this year, which is a Friday, you won't have much traffic in any of the cities, because schools are all out, and a lot of people will be taking the day off to make a 4-day weekend. So don't worry about fidning alternate routes; just take the shortest routes through each city.
I-295 around Richmond is usually better than I-95 through Richmond. It's smoother, has fewer interchanges, higher speed, more lanes, and far fewer curves and snakes that cause lower speed and accidents. Even though it's a little longer by milage, it's almost always quicker because of the higher speeds and straighter alignment.
Baltimore. I forget the number (695?) but there is a beltway that skirts around the horn through Towson so you avoid the midtown tunnel.
Washington DC. A lost cause. There are beltways that skirt around the horn but they're just as crowded. There are also routes like 301 and 13 through Dover DE and Newport News but I'm sure they are full of traffic lights so you won't save time.
I-695 (the Baltimore Beltway) is a roughly circular route surrounding the city of Baltimore. I-95 passes completely through the city like a slash from northeast to southwest. This makes I-695 seem like a viable alternate route to I-95 when passing Baltimore, especially when you see the construction going on at the northern interchange where I-95 passes I-695.
But in reality, taking I-695 is not a viable alternate route unless I-95 has an accident or other incident that really snarls traffic. Traffic on I-695, either to the east or west of Baltimore, is generally worse then on I-95, particularly during the rush hours, and the routes are both longer in both distance and time. Tune in to local radio stations and listen to traffic reports - I like Mix 106.5 for top 40.
As to DC, there are a few alternate routes, most of which take much longer and have a far greater chance of getting folks lost, but the best way to get through DC is to time your passage at night. Any time after 7pm and before 6am will do. If you can't time your passage at night, the next best thing is to do it during the slack periods between the rush hours, which would be 10am-3pm.