According to the Maternity Benefit Act, 1961 in India, the following rules generally apply regarding maternity leave:
Maternity leave entitlement
A woman is entitled to 26 weeks of maternity leave for the birth of her first two children. For the third child, maternity leave is reduced to 12 weeks.
In your case, since you are expecting your second biological child, you are entitled to 26 weeks of maternity leave regardless of the fact that you have a stepdaughter. The key point is that maternity leave is determined based on the number of biological children and not stepchildren or dependents. Since your stepdaughter is registered as your dependent in insurance, it doesn't impact your eligibility for maternity leave for your biological child. The law considers the biological children for calculating maternity leave eligibility, so you will be eligible for 26 weeks of maternity leave.
To summarize: For the second biological child, you are eligible for 26 weeks of maternity leave under the Maternity Benefit Act. The fact that you have a stepdaughter will not affect this entitlement.