Your liberal neighbor has "standing".
I didn’t see neighbors listed below. But, ‘for the children’, the neighbor will probably be included, in practice if not in the law.
“Colorado’s law, approved by Democratic Gov. Jared Polis, allows family, household members or law enforcement to petition a court to have guns seized or surrendered based on a showing that someone poses a danger under the “preponderance of the evidence,” a civil standard which means that the defendant is more likely than not to be a threat.”