Is it permissible for both wives to receive a monthly financial aid designated for families, if the husband owns two cars and each wife owns a car, knowing that one of the wives is not officially registered and that the state prohibits polygamy?

Grants and aid are only deserved upon the fulfillment of the conditions set by the granting authority. To determine if the conditions apply to the mentioned case, one should refer to the granting authority or ask those knowledgeable about the regulations and their conditions in that country.