If it were me, I couldn't NOT do something about it. What I would do, though, is drive back by there and try to get a better look. As long as they look like they have food and water, I would let them be, but try to keep checking back, so that the moment they start to look too malnourished, you can call the police - but you'll have to make sure not to take "we have higher priorities" for an answer. So, check back on them, and let us know if they appear worse.