<p style="text-align: left;">If they broke their fast knowing that they were obligated to fast then they must pay the Kaffara and make up the lapsed days. In addition to that, if they did not make up the missed days until the next Ramadan, then they must pay 900 grams of dates, wheat, floor, rice, lentils and the like to the needy people for every day that has not been made up.</p>
It is recommended to greet all Muslims whether they were practicing or not. It is better to offer help to believers whether they were practicing or not. Also it is better to socialize with people in good manner with people who practice Islam and with the ones that do not. It appears in some of the narrations that the good behavior deserves great reward.