If your husband was actually owed some portion of the $80,000, then he can hire a lawyer and "interplead" into the lawsuit by the union to protect his rights in the money. If he is not owed any portion of that money, then he has no standing to interplead, and no right to discover where the money went -- other than to the extent that any union employee may have in obtaining information concerning the union's activities (which is generally whatever is contained in the union's periodic reports to members).
However, even if your husband were not to interplead, the union will likely pay him what he is owed, unless there is some sort of fraud or embezzlement ongoing.
And, if your husband has evidence that the union is stealing from the members, then he can file a complaint with the National Labor Relations Board
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