DLA Piper (https://www.dlapiper.com/en) works with all of the specific groups mentioned below.
The DC Bar
Has an immigration referral clinic, and at the bottom of this page is a list of their various clinic partners.
The D.C. Bar Pro Bono Center, along with many partners, sponsors a quarterly Immigration Advice and Referral Legal Clinic to provide free consultations to area residents.
https://www.dcbar.org/pro-bono/what-we-do/immigration-legal-advice-referral-clinic
Ayuda
Provides direct legal, social, and language access services to low-income immigrants in Washington D.C., Maryland, and Virginia. A great local (DC/MD/VA) nonprofit that focuses on immigration, among other issues.
https://ayuda.com/legal-services-4/immigration-law/
The Tahirih Justice Center
A national organization assisting women, girls, and immigrant survivors of gender-based violence.
https://www.tahirih.org/
KIND (Kids in Need of Defense)
Focuses on children at risk from immigration policies and enforcement.
https://supportkind.org/
National Immigration Legal Services Directory
This is something of a clearinghouse of legal services providers in DC focused on immigration.
https://www.immigrationadvocates.org/nonprofit/legaldirectory/search?state=DC
DC Volunteer Lawyers Project
Provides legal services to victims of domestic violence, dating violence, stalking, sexual assault, and other forms of gender-based violence, and to vulnerable children living in dangerous situations.
https://www.dcvlp.org/