As per your query, if any person who is married, his wife is considered as a nominee. But if she remarries, then she is not entitled to receive the gratuity amount. In this case, parents are the legal nominees.
The share of gratuity is mentioned in the form that the concerned employee fills out at the time of joining. The percentage of the share is also indicated in this form. If the nominee is one person, then he/she will be entitled to 100% of the gratuity. If there are two nominees, then equal portions will be given.