What should I do when told "you should discipline them more strictly" or "they'll catch up eventually"?

Even words from good intentions can hurt. First receive it—"thank you for worrying"—while calmly conveying the facts: "this isn't a discipline issue; it's this kind of trait, and we're working on it this way with professionals." Rather than trying to persuade everyone, it's fine to draw a line if needed—"it would help if you could watch over us." Keeping connections with trusted people and professionals, so that you as a parent don't become isolated, matters too.