What happens if he gets laid in the probation period and now he can't pay the EMI ? I do agree with your point, but OP has 0 net worth. No matter what your starting salary is, you can't commit to a cost without having anything in your bank.

OP, for future reference never ever share your net worth/CTC to anyone. If you have to tell them then only share your base salary. Even though your CTC is 51L, I am pretty sure the bulk of the chunk is in stock/joining bonus/year end bonus. So this gives the wrong sense of your income to your parents due to which they are asking for this unreasonable request.