Brady Campaign sues to block Park Service rule
Yep, there might be some serious standing issues. Brady Campaign in itself, as a corporation, is not affected by the rule. It has to argue organizational standing, that it should proceed as a surrogate for its members. That requires it to show (1) its members suffer harm in fact (so broadly defined that, yes, they can easily show that. Just get some to say they'll quit going to parks that allow guns, or be apprehensive when doing so). (2) that the harm is "germane" to the organization's purpose and (3) individual participation is not required (again, easily shown).
(2) *might* be a problem. The purported harm in fact is that members don't go to certain parks, and Brady Campaign's purposes do not include getting people into parks. But there was, during my time at Interior, a ruling by the DC Circuit that held that HSUS had standing to sue over hunting in wildlife refuges (which allegedly left their members disgusted at gut piles, etc.) even tho it, too, was not a travel agency. The DC Circuit held that "germane" was a very broad term.