1. His second and subsequent marriage are illegal as he married without divorcing his first wife. Your mother can file a criminal case for bigamy against him. It is his inescapable duty to support his wife financially. To this end, your mother can file a case for maintenance against him in the court whereupon the court can direct him to maintain his wife.
2. However, neither you nor your mother has any rights in his self acquired or ancestral property during his lifetime. The only right which your mother has is the right to reside in her matrimonial home.