Since the Army personnel is deceased, there is no way to alter the Pension Pay Order (PPO) documents or the records held by the pension office. You cannot include the names of the dead wife, either the first or the second now. The changes should have been made by him, while he was living, as it was he who had been in service, and it is his pension. A third person is not entitled to initiate changes.
The service records should have the wife's name. Is the first wife's name showing in the records? When did he remarry? Was it after his retirement? If he had married the second time while still in service, he should have provided the second wife's name in the pension-related documents at the time of his release from service. The Services have made it mandatory for personnel to open a joint account, with the wife, for the pension payment. Check who is the joint holder in his bank pension account.
Family pension is given to the wife, unmarried dependent sons below 25years of age and, unmarried, divorced or widowed daughters as long as they are single and unemployed. Disabled children receive a pension for life. They must be from a marriage mentioned in the service record.
Check his PPO; it should have the name of the wife mentioned. Does it match the name of one of the dead wives? The pension document is very important. This piece of paper decides who gets the pension, provided the individual can prove their identity through PAN card or Aadhar Card.
This appears to be a tricky case. You can approach the Principal Controller of Defence Accounts (Pensions) at Allahabad or lodge a complaint on the official website (http://pcdapension.nic.in/pcdapension/compl/index.php). The other alternative is to fight a legal battle, provided the marriage can be proven, and there is nobody else involved. There should not be another wife, whose name shows in the records.
There have been cases where more than one wife shows up to claim pension and other benefits. Hence, retirement dues and pension are given only to the spouse or dependent children whose name appear in the pension documents.