Third party intervenors have Article III standing in an action centered on a consent decree where the intervenor claims that a likely improper enforcement of the consent decree will have adverse consequences for the funding of the schools that their children attend.
http://media.ca8.uscourts.gov/opndir/18/07/163437P.pdf
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.