Okay.  Here is the deal.  There is something called manners.  Manners suggests that it is polite to keep one's nose out of other people's business unless you actually know that person.  And even in cases where you are family or a close friend, you should really not say anything about people's lives unless they are hurting themselves and others.  

With regard to remarried people and Communion, one should refrain from lecturing someone about receiving Communion or go to the priest and tattle about Jane or John Remarried.  If you want to express the opinion that divorce is bad, that is fine for you to do.  But MYOB when it comes to individual remarried people and their participation in the Church including their reception of the Sacraments.