When an acerbic alcoholic finds himself penniless and alone he has no choice but to crash his family’s holiday. Years of alienating them makes for a stiff challenge, but eventually he subtly helps them heal.

I agree with the other comments here, but I would also take out acerbic. When writing a log line you want to use words that are so common people have no trouble knowing their meaning because these little snippets are for the general public. I have a pretty broad vocabulary myself but even I had to look up what acerbic meant. If I don't know, then other people wont either. Keep it simple.

The comments above highlight the issues with the log line. it feels very separated, like the first half and second half are talking about two different things. Does this alcoholic go on the holiday in the hope of getting some money, only to realise that family is much more important? If that is the case it should be saying that when he becomes broke he crashes the holiday to wiggle his way into the family money but along the way he realises the love of family means more?! I'm not sure if that is the sort of thing you are going for but these are the sort of things we need to know, nicholas' comment above gives some good points that must be included.

I have a concern about the vagueness of the logline.

What is the event that makes him realize how broke and alone he has become? Because if he's acerbic and has been alienating his family for years, why would he suddenly go: "You know what I need? To be around my family." What does he go to them for? Money, or companionship?

What then is he doing once he's with the family? Just kind of hanging around? If he's a very passive protagonist, you need to make clearer the antagonistic force he's going to face during the film, along with a clear indication of the stakes of failure in whatever he's actually doing.

The hook seems to be there - an alcoholic spends a holiday with his estranged family - so you've got that much clear.