I'd nominate:
{mouth_cover, hand_over_mouth} -> covering_mouth
{cover_eyes} -> covering_eyes
Hand_on_head, covering_eyes, and facepalm seem fine left as is.
I don't know that we should do any further unification grouping beyond that.
EDIT: Actually after checking, there are less than a handful of posts in cover_eyes, and mouth_cover, so I don't see that even an alias would be neccessary.
Hand_over_mouth however is a majority-use tag, in which case we might want to reverse the alias I suggest above.
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