I will clarify all your doubts.
First, bigamy case is a criminal case. If you can prove bigamy, he will be arrested and sent to jail. You will not get maintenance. It is not maintenance case. Even if you write a complaint to his office about bigamy, he will be in big trouble and he will be suspended and after domestic enquiry, he may be terminated from the services.
But, if you want to get maintenance, you have to file S.125 Cr.P.C. case and you will get that amount if you show that he is not giving proper maintenance to you.
In respect of his post retirement benefits, as long as he lives, he can enjoy them. After that, you are entitled to those benefits, irrespective of to whomsoever he nominates. But your adult sons are not entitled but unmarried adult daughters are entitled till their marriage.
I suggest you to file S.125 cr.p.c. in the present circumstances.