Concerned neighbor noticing increasing odd behavior but wanting to be respectful of privacy & dignity, looking for advice.

Hi,

My mom and I have lived next door to an elderly couple for about 3 years now. Over time, I've seen the woman doing a number of things suggesting to me that she is probably experiencing auditory hallucinations and perhaps some kind of paranoia, or other delusional thought process, or highly unusual thought process at least. She and her husband both seem to be somewhat unusual and mainly keep to themselves, though very rarely now and then have conversations with another neighbor on the street, and every once in awhile I've seen a couple people visiting them who seem to be family. It's often unclear to me if both husband and wife are engaging in some of the odd behaviors together (all of this is stuff happening on the street/sidewalk by the way), but more frequently I just see the woman doing this (though I think both spend most of the day at home).

What's prompting my concern is just that the woman seems to be doing these things that seem odd more and more frequently. The behaviors change with time but at present she is going around over and over to the same locations on the street and staring very intently at particularly things for quite some time, sometimes speaking softly and tersely on and off, and will do this for quite a long time (over and hour or more) on most occasions, and repeatedly throughout the day and into the evening, on most days. I haven't seen her go into anyone's yard but she does go right up to stare at things. Some times maybe taking pictures.

As far as other possibly relevant indicators, their house has significantly unkempt foliage of all kinds in front and back (like to the point of appearing quite chaotic with a fairly unusable backyard) but not unsafe per se. They are always timely with bring trash, recycling, and compost bins to the curb and back each week. Very rarely I see the man driving their car.

It's really mainly the increasing frequency and amount of time spent on the behavior that's worrying me. It's easily apparent so that if I have anyone over they almost always ask about it at some point. My mom is worried too and has experience in a mental health triage setting (I have some experience around clinical social work).

Basically I don't see any signs suggesting abuse or self neglect, and I have no idea anything about my neighbors aside from observations. We had a brief conversation once, prompted in fact by something I was doing at the time which understandably might have appeared quite odd (sprinkling diatomaceous earth to prevent pests around our building on advice from a professional), which is also to say, I definitely don't want to put myself in a position of presuming to define odd vs normal behavior. I want to respect their privacy & dignity as individuals & as a family. I definitely don't want to cause unnecessary intervention into their lives. I also don't want to sit idly by while someone's mental state deteriorates to an unsafe condition if there are clear signs (now or in the future) that show a line is being crossed.

I'm not asking anyone to assume the role of expert but just wondering if anyone can share some advice, broadly speaking. I wish I had the sort of neighborly relationship where it wouldn't be abrupt to suddenly go over and check on how they're doing, but that's not the case. However if it seems warranted I would want to figure out how to go about doing this. The easiest advice to receive is basically stop overreacting and mind my own business, but I just wanted to try to reach out somewhere and ask.

Thank you, I welcome thoughts and questions, I apologize for not providing a more concise question.