You should consult a local attorney. However, it appears the first wife may not be entitled to any of the pension.
Unless your husband had already retired before the first divorce, then the first wife may have never been entitled to 1/2 of the pension.
Generally, if the husband has a retirement account that he made contributions to for 30 years and was married to the first wife for 10 of those years, as an example, then the first wife could claim 1/6th of the pension. That is calculated by taking the number of years of the first marriage
and dividing that number by the total number of years of contributions, which is 30. So 10/30 equals 1/3.
Then the first wife would have a claim to 1/2 of the pension that accrued during the first marriage. So you would divide the 1/3 by 2 which would show the first wife would have had a claim to 1/6th of the pension.
You will have to do the calculations based on the specific facts of your husband's case, but since the first wife has been paid, apparently for many years, she may have already received more of the pension than she would have "legally" been entitled to.
There are other issues related to whether your husband should get credit for the payments made to the first wife, but he still has valid claims that the first wife is not entitled to any more money.
Please follow up with a local attorney. Please let me know what questions you may have as I want to be certain you are satisfied with my response so that I may be paid.