Great news about the babies, bad news on the timing.
I understand COMPLETELY about the mother-in-law demanding you to be present.  
Mine is a nice person, but doesn't feel complete without all her boys at 
certain events.  I occasionally  send Bruce without me (I work for a company 
where the last 4 weeks of a quarter are too wild for me to take a weekday 
off), but I don't think this would work for Christmas.
Options:
   Change religions
   Change husbands
or, pray for a highway shutting snowstorm!  (less controllable, less 
long-term impact.
;)
--- MacWoof 1.5.3
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