Can a couple that is separated benefit from the exemption from real estate capital gains tax on the sale of their principal residence?

  Yes, both members of a separated couple can benefit from the exemption in respect of the sale of the principal residence even if one member of the couple continues to live in the property. The exemption is subject to the fact that the property really was the couple's principal residence until the time of separation and that it subsequently continues to be the main residence of one member of the couple.