When in doubt, report. Let Child protective services make the call. Here kids are taken(or.arranged to stay with relatives if at all possible) on a temporary basis and help provided for filthy environments. It has to be a health hazard (feces, urine, very old food particles in various places, etc)and not simply untidy. I say, personally, not to try to evaluate. Child services usually does NOT want to take the kids and punish people and almost always offer help first. My husband is a child welfare lawyer and there are times when help is granted instead of punishment and hoarding can be part of a mental illness. Courts want parents to have their babies when drugs are not involved or abuse. The couple will likely get checked and given X amount of days to fix the problem . So go ahead and report and don't worry about anything else because child services is used to "false alarms" and they will investigate. Don't stress about investigating and being the judge yourself. That's too stressful and you have other jobs to do and people get paid good money to do all that stuff.
Contact your local bar. They can help you.