Starring Robert De Niro and Diane Keaton. Rated PG. Now playing

While you’re watching The Big Wedding, the hardest thing to marry is the fussy, Better Homes setting and raunch that often verges on the Farrelly. Talk about disconnect. When Robert De Niro’s Donald isn’t talking about “poon jobs” or calling his ex-wife the C-word, he’s doling out fatherly life advice to his adult children. What you end up with is a strange combination of the sickly sweet and the sick—with a lot of silly, strained jokes in between. Oh, and a lot of people falling into swimming pools and lakes.

If The Big Wedding simply aspired to the cynical lows of Focker-dom, it would be fine, but it wants to carry more sentimental messages about how much family members really love each other, even when they’re barfing on each other or complaining about cock-blocking. This amid the perfect flower arrangements, white lawn tents, and lakeside setting of just about the most elaborate, expensive matrimonials you’ve seen since Four Weddings and a Funeral (which, come to think of it, probably started it all).

The story, writer-director Justin Zackham’s adaptation of the French comedy Mon frère se marie, basically centres around divorcees Ellie and Donald (Diane Keaton and De Niro). They can’t stand each other—Donald’s living with Ellie’s former best friend Bebe (Susan Sarandon) now—but they have to pretend they’re married again for the wedding of their adopted Colombian son Alejandro (Ben Barnes) to Missy (Amanda Seyfried). You see Alejandro’s birth mother is a strict Catholic, and… Oh, never mind.

The plot is ridiculous, but you can’t really complain about the comic acting here; we are talking about Keaton, De Niro, Sarandon, and a suprisingly dialled-down Robin Williams, after all. Even the younger cast, from Topher Grace’s deadpan 29-year-old virgin to Katherine Heigl’s refreshing turn as an embittered divorcée aren’t bad.

But sorry, folks: a bunch of crude jokes can’t liven up a tired dysfunctional-wedding story, and neither can a cast that includes Godfather actors.