I don't understand posters telling you to "leave it to them" or "stay out of it" as it sounds like a dreadful situation to have to encounter on a daily basis. Hopefully the guards will take the appropriate steps to sort whatever peculiar issues your neighbours have, but just on the part-quote above of what you said I would consider contacting the local Environmental Health officer (your local council will direct you to the right person). I don't know if they deal with domestic issues but you may get some useful advice.