"Pardon me, but, when is Nisan 14 this year "
Nissan 14th will fall on April 17th - but there's no guarantee that's when the memorial will be. Last year they held the memorial on a day that was actually Nissan 15th or 13th (can't remember which direction now but it was off a day). I questioned that when my mom invited me last year - never did get a good explanation except it had something to do with how their calculations of the calendar were more accurate than the Jews calculation of their OWN calendar so the jews were celebrating passover on the wrong day (bwaaaaaaaaaaaaaaaa) ..........seriously - that's the answer I got.
As for what will I be doing? I celebrate the Lord's Supper by partaking just like he offered to all who would follow him. I say a prayer and thank him for all he's done - and enjoy the unleavened bread (I buy mine in a store) and some really good wine.