Marrying a Mennonite Christian

Assalamu Alaykum.  May Allah (SWT) bless you for this wonderful service.  I will try to be brief.My newphew is marrying a mennonite this fall.  This has caused quite a stir in the family as she is not converting and this is okay with my nephew .  However, we have accepted her at family gatherings and will pray for her reversion while trying to do da'wa (when and if we are given the opportunity).My brother and his wife will be having an elaborate wedding for them (over 300 people).  I have told my parents (the groom's grandparents) that I will not attend as I cannot morally celebrate my nephew marrying a non-muslim.  I also have to be an example for my own sons that this will be unacceptable to me if they follow the same path.  I do not want to be a hyprocrite to them i.e. "do as I say, not as I do".  My parents are insisting that I attend.  If I do not, I am sure that the relations with my brother's family will be completely cut off as they have expressed this to everyone in the famil.  However, I feel that is the price that may have to be paid to stand up for my principles and deen, and as a parent.The wedding will be mixed with music and dancing - I cannot use this as an excuse not to attend as the last wedding I attended was of this nature.  Please advise me what to do - will I be disobeying my parents if I do not attend or will I be gaining the favour of Allah (SWT) and setting my children on the right path?  I do not want to displease my elderly parents, but I fear that my children's future is at stake.Also, there are unconfirmed rumours (which I will bring up with my brother shortly) that her 'pastor' will "bless" the marriage.  Might I add that the local Imam will not officiate at their wedding.  We hear that an "imam" without proper certification to marry people in Canada will do the "nikah".  We have no idea about the civil ceremony.Forgive me for the length of this question.  I am eagerly waiting for your reply.Jazakum Allahu Kheiren.