In this TV-movie, Robin Sachs plays Coplann, a member of the Minbari Grey Council. In an episode of "Star Trek: Voyager" (1995), Sachs plays an alien named Valen. In B5, Valen is the name of the Minbari holy figure who originally formed the Council.
The backstory on the Centauri woman is that her name is Senna. She is Emperor Mollari's ward. Her father was Lord Refa, whom Mollari had killed.
Both the children and the Centauri woman are members of Emperor Mollari's household, and all got there through murder. Luc and Lyssa are the niece and nephew of Urza Jaddo, whom Mollari killed in a duel in the Babylon 5 installment, Knives. Senna, the Centauri woman, is the daughter of Lord Refa, whom Mollari had assassinated in the installment, And the Rock Cried Out, No Hiding Place. In both cases, Mollari took the children of his victims into his family.
According to Babylon 5 canon, Senna later marries Vir Cotto. When Vir becomes emperor, she reigns also, as empress.