I recall from the Animal Park show that these sisters were from France and I believe, not sure if it was from later in series or not, that they may be amongst those related to the tiger (Roman?) found to have Sumatran genes. i may be wrong tho
They are indeed three sisters from France. Named Svetli, Shouri and Soundari. They came to Longleat in November 2006 having been born at Mulhouse Zoo in 2005. They were believed to be pure Amur's until 2007 when the hybrid gene was discovered. Hence they have been removed from the studbook and are being used as an exibit only group. (no breeding in other words)
Longleat kept one white tigeress (Chandi), a normal coloured female Bengal (Kaduu) and a male Golden Tabby called Sonar before the current three arrived. Chandi was put down in 2004 due to cancer. Sonar died of old age in August 2006, Leaving Kaduu on her own until the new cats arrived. Kaduu's health went downhill in 2007 or 2008 and she was put to sleep.