The couple were apparently well known in the Brixton communist scene during the 1970's and that seems to be how they gained cult-like control over the two older women.
The 73-yr old man is Aravindan Balakrishnan, aka Comrade Bala, an Indian national who at one time served on the central committee of the Communist Party of England (Marxist-Leninist) before splitting to run a Maoist commune.
The 67-yr old woman is his wife Chanda Balakrishnan, aka Comrade Chanda, a Tanzanian national.
There are also reports that the 30-yr was "adopted" after her parents died in a fire, also that she sent love letters to a neighbour where she disclosed her status as slave but he did not report it, and threatening letters to his girlfriend who also did not report those. That comes by way of the Daily Mail though, so pinch of salt.
Edit to fix the broken links