Alexei and Sergei Tkachev

Alexei (or Aleksei) and Sergei Tkachev were brothers who collaborated on their paintings. There's a good summary of their work here (you need to scroll down a ways to find them).

 Children (1960)

 Curious Onlookers (1962)

 In the Bath (1974)

 Laundresses (1956-57)

 On the Veranda (1987)

 Spring

 The Postgirl in Winter (1951)

 Windy Day (1957)

Between Battles (1958-1960)