The other candidates can meet the criteria for Article III standing because they can demonstrate DIRECT injury-in-fact from an ineligible opponent: Trump and Kaisch would always have standing to bring an eligibility lawsuit. They could even be lead plaintiffs with other citizens (registered Republican primary voters).
So if Kasich and Trump can be lead plaintiffs with other registered Republican primary voters, can't these registered voters be the lead plaintiffs?
Forgive my ignorance, and thank you in advance for explaining it.