Oswald Adalbert Sickert (b. ca 1828), an artist and musician, and Eleanor ('Ellen') Louisa Moravia, his wife (b. ca 1831 - d. 1922), were born in Germany (Oswald was a naturalised British subject). Their children included Walter Richard (b. 1860), Robert (b. 1861), Bernhard (b. 1862), Helena (b. 1864), Oswald Valentine (b. ca 1871) and Leanhard (b. ca 1873). In 1881 they were all, except for W. R. Sickert, living at 12 Pembroke Gardens in London.
Bernhard Sickert was a painter of landscape, still-life and interiors. He took up painting as a career around 1885 and he exhibited at the RBA (1885-1888) and the New English Art Club (1888-1909). He also exhibited at the Royal Academy and the Grosvenor Gallery.
He seems to have been in contact with JW around 1899-1902 when he approached him about a small monograph (see #05419). However it was not published until 1908, several years after JW's death (Sickert, Bernhard, Whistler, London and New York, 1908).
UK census 1881 at http://www.familysearch.org (accessed 2004.9); Bénézit, E., Dictionnaire des Peintres, Sculpteurs, Dessinateurs et Graveurs, 8 vols, 1956-1961; Wood, Christopher, Victorian Painters, 2 vols., 3rd edn., revised, Woodbridge, Suffolk, 1995; Johnson, J. The Royal Society of British Artists 1821-1893 and The New English Art Club 1888-1917, Woodbridge, Suffolk, 1975, 1993 edn.