Smalltalk suggestions for a horrid gathering?

As you obviously care about your father...focus on HIS happiness rather than your discomfort. Remember that their behavior is plainly visible for all to see... as yours is. Be the very best you can be...and that's what his memories will hold. As for small talk...keep it small. Avoid criticism and be polite and respectful. Be positive in your responses. Be brave...nothing lasts forever and the more effort you put into enjoying yourself under ALL cirstances...the happier you will be! Bless you and Merry Christmas!!!!