What you have mentioned to me, or how I’ve understood it, is that you’re attending gatherings wherein Jesus (sws) was being described as the son of God. You had to stand in respect at what they were singing. Knowing that what they were singing is shirk, at least a part of it, I think you shouldn’t participate in the ritualistic activity that they are conducting. You ought to either find ways of gracefully dissociating yourself from what they are doing at that time or else not go there at all. As for their good people, you must find ways to talk to them on other occasions.
Many people are following their religions sincerely. That doesn’t mean that we should join them in what they are doing. When we know that it is wrong to ascribe partners to God, if any such act is being done, I wouldn’t like to be a part of it. If the person doing it is sincere, he/she will hopefully come out of it, not necessarily because of me joining him/her in the act.
I have a fear that joining them while they are doing things so clearly wrong would start affecting my feelings as well. I have to be careful about my religious feelings, first of all. No compromises on that.
To summarize, I feel there’s no harm attending their sessions, provided you have decided to talk to them about the Islamic view, at some point, in mind. Be a little careful, but I wouldn’t discourage you. It gives you a reason to know how others think. Don’t participate in anything that amounts to a religious ritual. It should only be for learning purposes and enabling others to come close to you.
Courtesy: http://www.islamicissues.info/qa_question.php?qid=396