Standing to bring your suit is the Plaintiff's burden. "Standing" has various legal meanings so I am answering it based on an individual's right to pursue a claim. An allegation of lack of standing can be an affirmative defense challenging the Plaintiff's right to bring suit at all. This would require proof by the defendant, but only after Plaintiff can successfully establish standing. The same evaluation applies to an intervenor. The intervenor must allege standing and you can challenge it as another party.
The answers given are limited to the facts as given and presumed by the answer itself. Without seeing actual written documentation or having a conference to more fully explore the issues, this short answer has only limited application. Make sure to seek legal counsel and provide all documentation to get assistance in making informed legal choices. Bstein@dcfsz.com, 305 377 1505