Lyndon Sheehan and his sister, Amy Sheehan, will both compete at Sochi in freestyle halfpipe, but not for the same nation. Lyndon will represent New Zealand, while Amy skis for Australia. Apparently Olympic News Service (ONS) just announced that this is not rare, and  happened twice before at the 2010 Winter Olympics, with brothers Jan (NOR) and Tommy Schmid (SUI) in the nordic combined, and siblings Anastasia Kuzmina (SVK) and her brother, Anton Shipulin (RUS), in the biathlon. ONS missed another one from Vancouver, as the Reed Siblings, Allison (GEO), Cathy (JPN) and Chris (JPN) all participated in figure skating.

But it actually first happened back in 1960 at Squaw Valley. There František Tikal played ice hockey for Czechoslovakia, while his brother, Steve Tikal, played for Australia, and they played against each other.

Here are the siblings who have competed at the same Winter Olympics, in the same sport, but for different nations:

1960: František (TCH) / Steve (AUS) Tikal in ice hockey

1998: Hans (AUT) / Bernard (SLO) Knauß in alpine skiing

2002: Robert (CZE) / Martin (GER) Reichel in ice hockey

2010: Jan (NOR) / Tommy (SUI) Schmid in nordic combined

2010: Allison (GEO) / Cathy and Chris (JPN) Reed in figure skating

2010: Anastasia Kuzmina (SVK) / Anton Shipulin (RUS) in biathlon

But it has also happened a number of times at the Summer Olympics, as follows:

1964/1968: Fred (NED) / Tony (USA) van Dorp in water polo

1984: Carmen Ionescu (CAN) / Florenta Tacu (ROU) in athletics

1992: Katerina, Maggy (BUL) / Manuela Maleeva (SUI) in tennis

1996: Gusman (MDA) / Elmadi (KAZ) Zhabrailov in wrestling

2000: Jenny (ITA) / Jessica (NED) Gal in judo

2008: Ágnes (HUN) / Erszébet (ITA) Valkai in water polo

2008: Hilda (NED) / Sylvia (KEN) Kibet in athletics

2008: Matty (USA) / Shane (NZL) Reed in triathlon

2008: Natasa (HUN) / Stjepan (CRO) Janic in canoeing

2008/2012: Soslan (UZB) / Taymuraz (KAZ) Tigiyev in wrestling

2012: Mimi (BRN) / Almensh (BEL) Belete in athletics

In addition to the Tikals competing directly against each other, this also happened with the Van Dorps in water polo in 1964; the Reichels in ice hockey in 2002, and the Valkais in water polo in 2008. In addition, the Zhabrailovs actually had a wrestling match against each other.

UPDATE (9 July 2016): As the 2016 Olympics are dawning, the brother / sister tandem of Bernard Legat  and Violah Cheptoo Legat will also compete for different nations in Rio. Violah has made the Kenyan team in the women’s 1,500  metres. Bernard made his fifth Olympic team at the US Olympic Trials in the 5,000 metres. He competed for Kenya in 2000 and 2004 and for the United States in 2008 and 2012, and to come, in 2016..