If they lived in Wilno (Vilnius) maybe you should refer to the Vilnius Regional Archives:
collects and stores the postwar resources of state institutions, local government, NGOs, civil society organizations, individuals from Vilnius district (Vilnius city, Vilnius region, Šalèininkai District Municipality, Svencionys region, the area of Trakai, Širvintos District Municipality, Ukmergė District Municipality, the city Elektrėnai) and conducts exploration, issues certificates and other documents concerning ownership issues, housing, seniority and other from the postwar period to the present day.
Archival services are payable in advance and depend on the type of extracted documents.
Look at this site (available only in Polish)
wilno.msz.gov.pl/pl/informacja_konsularne/sprawy_prawne/dokumenty_archiwalne/dokumenty_archiwalne
and here - Office of the Chief Archivist of Lithuania:
archyvai.lt/en/genealogical-search.html