When a charming con artist settles down with a sweet yet gullible woman, he must spend Christmas with her dysfunctional family – and unexpectedly experiences the concept of family for the first time.

In your last logline, it looks like you gave away the ending, something a logline should never do.

Beyond that problem, where is the conflict? Since the con artist is the MC, the conflict within the dysfunctional family does not count. The logline needs to tell us what conflict involves the MC. If the MC is simply observing the conflict, then he is not the MC. (In the "Great Gatsby" Carraway narrates the story, but Gatsby is the MC as he drives the major conflict.)

Okay...

Perhaps this one?

Trapped in his old hometown during a snowstorm, a charming con artist must spend Christmas with a dysfunctional family - and unexpectedly finds the family he never had.

(27 words?)

Very long version: (yeah I'm gonna try to get this to under 25 words. Still playing around with it.)

Trapped in his old home town during a snowstorm, a charming con artist settles down with a sweet yet gullible woman for the holidays, but must spend Christmas with her dysfunctional family - and unexpectedly falls in love with the family.