Sweetie sounds a bit like The Hanging Garden... A gay son, alcoholic father, a disturbed mother, a grandmother with end-stage Alzheimers (the family keeps her locked up), even their dog is almost blind and constantly walking into walls and tables.
It's one of a very few films I can't bring myself to watch a second time. The writer's intent was to create something that defies all attempts at categorization, and he succeeded IMO. I'd call it something between comedy and horror.