After a sequel and a spin-off (“The Minions Movie”), the “Despicable Me” franchise shows no signs of slowing down, let alone ending, and this third installment moves the property further into the territory that most animated films occupy nowadays—a celebration of family. In the first movie, comic villain Gru (voiced by Steve Carell) mellowed and adopted three little orphan girls. In the sequel, he found his soul-mate and got hitched. Now he finds that he not only has a brother he never knew about, but a twin to boot. One can only wonder how large the brood will become as the series continues; perhaps a future installment will center on his bonding with a third cousin, twice removed.

In any event, this third picture suggests that despite (or perhaps because of) the increase in the number of characters, the series is getting tired. It doesn’t lack action, but even the hectic scenes are curiously flaccid, and much of the rest of the movie drips with stodgy sentimentality. (The intensity with which the script tries to extract “Awws!” from viewers is so pervasive that even the makers feel obliged to make fun of it in a scene toward the close.) The result is a movie that’s running on fumes, dependent on the good will viewers might bring from their recollection of its predecessors.

It’s also a choppy affair, consisting of a bunch of largely separate storylines that proceed in tandem until they all come together at the end—an arrangement that results in characters disappearing for long stretches while others come to the fore. The scene is set when Gru and his new wife Lucy (Kristen Wiig) are fired from the Anti-Villain League by their screechy new boss (Jenny Slate), for their failure to capture the movie’s villain—an ex-TV child star named Balthasar Bratt (Trey Parker), who’s out for revenge against the world in general, and Hollywood in particular, for his show’s cancellation thirty years ago. His plan involves the theft of a giant diamond, which will power a robot that will demolish California with super-strong bubble gum and laser rays.

The now-unemployed Gru soon learns that he has a twin brother named Dru (also voiced by Carell), a supremely wealthy goofball who owns a huge pig farm in the Marx Brothers nation of Freedonia. Gru will go to visit him and learn that the guy has always wanted to be a super-villain to follow in the footsteps of their father, and he asks Gru’s help to become one. Eventually, despite occasional roadblocks, they will bond in the effort to foil Bratt’s terrible scheme and save his potential victims.

Those include Lucy and the three adopted girls—Margo (Miranda Cosgrove), Edith (Dana Gaier) and big-eyed, unicorn-obsessed Agnes (Nev Sxharrel)—who go off pretty much on their own in Freedonia and get involved in a series of largely independent adventures. If the theme of the Gru-Dru episodes is fraternal bonding, the one here is Lucy’s learning to become a true mother to the kids.

Then there are the Minions, most of whom rebel at Gru’s refusal to be a villain anymore and go off on their own. Much of their material—involving a stint in prison and an elaborate escape sequence—is completely distinct from the main “plot,” feeling almost like little shorts simply dropped into the picture to feed fans’ expectations. Even when they show up at the end to help Gru and Dru, the little yellow munchkins are peripheral to the main action.

The result is a movie that lurches ahead in fits and starts. Is it amusing for a bunch of Minions do a Busby Berkeley routine while singing Gilbert and Sullivan in their nonsensical gibberish? Sure. Is it funny for Lucy to push Margo into dancing with a forlorn Freedonian boy, only to find that doing so is the equivalent of a marriage proposal? Maybe, if a trifle odd (and leading to nothing). Are “dance fights” hilarious? No more than they were in “Daddy’s Home,” so let’s include a couple of them anyway. One expects digressions in a picture like this, but as it’s structured, “Despicable Me 3” often seems to consist of little more than endless digressions strung together.

Perhaps that’s because the central plotline of Gru, Dru and Bratt is frankly a bore. Even Parker can’t do much with a character whose sole distinction is that he’s still living in the eighties. True, there’s some amusement in the clips of pop tunes from the period that are periodically inserted into the action, but only for adults—the references certainly won’t be appreciated by the kids.

Still, despite all the clichés and defects, “Despicable Me 3” boasts characteristically lively animation from Illumination, and the affection audiences have built up for the characters over the years will probably induce them to overlook the fact that it’s a pretty undistinguished movie, one that actually suggests the series might deserve to suffer the same fate that “Evil Bratt” did in the 1980s. It won’t, of course—maybe that third cousin scenario is already on the drawing-board.