There are plenty of people who attend Young Israels who really arent that religious. They basically keep shabbos more or less and keep kosher more or less, but dont do much else.
The women do not cover their hair outside of shul and wear pants and the men do not daven during the week. Pretty much everyone in shul knows these people.
You can either tell them what they are doing wrong and risk they leave (and that does happen) or let them continue what they are doing as most do go to shul on shabbos on a regular basis and send their kids to day schools and live in a jewish area