We're also in NE DC. Here are two other options not yet mentioned:
A1 Stroke School (at an elementary school in Takoma Park, so not too far). It's once a week and small group instruction. We liked the instructors, but my kids were a little advanced for it (after 3-4 years of summer swim)
https://www.aonesportscoaching.com/a1strokeschool
Patuxent Aquatics Club (one practice site is UMD, so 20-25 min from NE depending on where you live). It's 2-3 days a week, but pretty chill on attendance. Lots of water time, nice coaches, and much more laid back (and cheaper!) than other competitive teams in the area - although a bit of you get what you pay for vs instruction from an NCAP or Machine. It's been the perfect situation for our family given the cost, chill nature, and fun incentives (they're much more about encouraging trying new events and improving your own times throughout the season). You also pay month to month so you don't have to commit to the full year and can stop if it's not the right fit.
https://pac.venitsports.com/