No one is saying they have no standing to sue.
I would say they have no standing to enter the US illegally. But that is just me.
The existence of signed consent forms are a basis for affirmative defenses of informed consent, waiver, and release. In this case, the affirmative defenses should be a quick winner, if the Court does not find any factual issues with the forms. If they do, then the factual issues of the defenses must go to trial, which would take awhile