A con artist spends Christmas with a family he grows to love, but his masquerade is threatened when his ex wife moves in next door.

Perhaps it's better like this...

A con artist spends Christmas with a family he grows to love, but his masquerade is threatened when he finds out his real family lives next door.

"Moves in" is doing too much I think.

Also, I kept in masquerade (it's doing double time here) so you know he's hustled them or ya' know seduced them into it. He is pretending to be someone else but I don't have time to put it in there.

This is the one I'm considering going with:

A lone wolf con artist seduces a woman by pretending to be someone else, but must first spend Christmas with her family, whom he grows to love.

It's simple and basically the film. But I want to lean in on the conflict. Regardless, I think his ex-wife and daughter are definitely a complication to deal with. His real life bleeding into the false one (that he wishes was real).

Not only that, I thought the setup/opening hook we've got him trying to call his estranged ex-wife and daughter - who don't want to talk to him.

This leads him to seducing a woman (and basically her family) and getting invited to spend the holidays with them.

Would the ex-wife really be moving house over Christmas? The time period seems very confused - how long did you envisage the film covering?

It would be great if you could keep updated versions of your loglines within the initial post so readers/commenters can see the evolution of the logline and the related comments.