Mohini is mother-in-law of Sunita and grandmother of Nanu. Vinod is grandfather of Tanmay. So, Nanu and Tanmay represent third generation.
Mohini and Vinod form a couple and represent first generation.
Clearly, Roha and Sunita form the other couple and represent second generation.\
Rohan is a CA. Since engineer is married, so Vinod is an engineer and likes red colour.
Mohini is a teacher and likes orange colour.
Nanu likes blue colour.
Tanmay is a Principal and likes black colour.
Sunita, Nanu’s mother, likes white colour.
Clearly, Rohan likes green colour.
There are three ladies in the family -- Mohin, Sunita and Nanu.