The duo singing started from the time of Mukta and Brinda (hope I am correct) and was popularized by the Bombay sisters. After them the successful pairs are the Priya sisters, Hyderabad brothers, violinist Kumaresh and Ganesh, flautist sikkil sisters and the most popular ones in the recent years, Ranjani and Gayathri.
Singing the kritis together is easy to some extent. Even in that singing different sangatis with uniformity is quite difficult. Though the aalapanas are sung seperately, I always wonder that how do they make it with the kalpana swarams. Is that easy to have a similar ‘Manodharma’ which is said to be the vital part of a concert? Even if they sing the kalpana swarams separately, but at one point they have to sing it together. Is that not a difficult task to coordinate?
Personally, I have observed many a times that my sister and me have convergent and coincidental thoughts. May be this is what is genetic advantage that the siblings have. But still I Wonder, How Carnatica brothers do it?