Many renowned classical piano duos have kept it in the family — consider the Labèque sisters, the Pekinel sisters, or the Kontarsky brothers. The vast benefits of a musical partnership between siblings were obvious during Christina and Michelle Naughton’s concert with The Gilmore’s Rising Stars Series yesterday. The two 28-year-old pianists brought esoteric unity to their art form in a way only identical twins can. But as their spellbinding Sunday afternoon performance showed, the Naughton sisters are no gimmick. The two extraordinary musicians demonstrated uncanny harmoniousness and technical precision, even when expressing individual soulfulness and spontaneity across two separate Steinways.