No, its not enforceable. The “underage” thing is (parental consent applies to a marriage, and these aren’t legal marriages). Thats about it. And thats about as far as the public ought to have any interest, that and the issue of force, where force is an element in maintaining control.
Texas over-reached. But where they can prove under-aged relationships, they may still have a case. And thats the only area where there is a public safety issue.
My understanding is that the guys have one “legal” wife, theoretically that one could be underage with parental approval.
BTW, what is the government doing in the deciding who can get married business in the first place?
Isn’t marriage a religious imperative?