For years, at school, I was forced into taking part in various "Productions". I found them acutely embarrassing and swore I would never attend one voluntarily thus I have stuck out against two wives, five children and four grandchildren and I will not attend any such event. That's me ~ learn to live with it or p*ss off has been my message throughout the last 40 years (Yes My eldest is now 40).
I was taken to a panto by my parents when I was about 8 and they had this so called comic on stage with a mirror. The trick was that he would reflect the spot light onto a child in the audience and said child would rise, go up on stage and sing with the "comic". Of course there was a bit of "banter" that went with this ~ all seeming to me to centre on some deformity that the "comic" saw in the child. Short haircut, sticking out ears, red face ~ in short anything he could take the p*ss out of. 20 children were chosen and I sank lower and power into my seat just knowing that he would pick me out and dreading the "encouragement" that my parents would give me to go up on stage. Sure enough it happened. The light shone on me and I refused point blank to join in the "jolly japes". My mother urged me to go on stage, My father swore at me but I sat tight. That night I was told in no uncertain terms that I was selfish and had ruined "their evening". I have never attended a panto since. Wild horses would not get me through the door. They are the most puerile form of entertainment known to man ~ beating even "I'm a so called celeb ~ what the f*ck am I doing here" etc.
I have steadfastly supported any of my children who do not want to perform at school or anywhere else ~ despite the claim that such performances are an essential part of the National Curriculum ~ utter bollox by the way.
Growler has to live with these people but in his position I would stick to my guns and have nothing to do with the "organised event". By all means buy your SiL a card and gift and give/send them to her personally but do not be forced into doing something you don't want to do.
As a PS: It was from that evening that things between my Father and I went downhill, culminating in my leaving home and joining the RAF aged fifteen and three quarters just to get away from home. He never forgot nor forgave me for "wasting his money" by refusing to perform when requested to at an event that I never actually wanted to see in the first place. Twenty years on he would still relate the tale of how I had embarrassed the "whole family".
Stick to your guns Growler ~ at least you will know you did what you felt was right and more importantly what you wanted to do. Let them call you names if they wish but Christmas is coming and they'll all want money from you no matter how "upset" they are so they will come round first ~ even if it is with their begging bowls as usual.