In your husband's movable (insurance amount as well as company entitlements like PF, gratuity and remaining salaries and if there is pension that also), car, scooter etc. and immovable property like plots, house etc. as per law, you, your children and his mother have got equal rights. Insurance company has done wrong. Even your in-law's name is there as nominee, Insurance company is not entitled to release that amount depriving you and your chlldren of your legitimate share. Same is the case in respect of office money. NOW WAHT YOU HAVE TO DO IS:
1. Write a letter to the office as well as insurance company to give you your share. Send this letter in Regd. Post, giving them 15 days time. I am quite sure they will not respond.
2. Engage an advocate and file an application under Indian Succession Act to issue you and other legal heirs succession certificate. In this case, if you have children, you and your children should be made applicants. You have to make Insurance Company and the office in which your husband worked along with the inlaws (if father-in-law has taken insurance money, he himself and your mother-in-law (she is also heir) be made respondents. You and your children will get your legitimate share out of his income including the insurance amount already drawn by your in-laws.