I'm sorry to know about your plight. In my view, you need not worry as you have every legal right to claim your husband's benefits (I presume your husband is no longer alive). Legally, the nomination given prior to the marriage of an employee becomes void after his/her marriage. You can read more about it in the attached article, which will hopefully give you some more hope.
Despite your legal rights, I have a few suggestions for you, considering the threats you are facing from your in-laws. This is purely to help you avoid any potential litigations and save time and money involved in such disputes:
1. With the help of elders in your family circle, try to impress upon your in-laws your legal rights and reach an amicable settlement acceptable to you.
2. Immediate actions to take:
i. Send notices to all the concerned officials stating that you are the legal wife/heir, acting on behalf of your children, and that all benefits/payments relating to your husband should only be settled to you. They should not act based on the old nominations filed by your husband prior to your marriage.
ii. File claim forms (in the prescribed format) with the concerned officials for PF, Gratuity, leave salary, salary dues if any, Insurance, etc., and ensure you carefully obtain acknowledgment of filing these claims.
3. As a precaution, immediately file a petition in the appropriate court and obtain a stay/injunction against any payment of your husband's benefits. This will prevent any early disbursement based on the previous nominations.
4. Also file a petition to obtain a "succession/legal heir certificate" in your favor (including your children, including minors, with you as their guardian).
5. You may seek the help of an advocate throughout these processes to avoid any issues.
Wishing you all the best.
Regards,
Kumar S.