There are several example in the rural areas of india where there are more workers in the family but gross income is low how do you explain this paradox

See it does not mean if you have more people working in family then gross income will be high too. For example, there 6 member in the family out of which 4 members are working and they have one hectare of land. However, the land can be easily handled by 2 persons. This means that the produce that 4 individual brought can be even be brought by only two individuals. So even if the number of workers are four but their earnings is same as that of two person. This is a case of hidden unemployment.