There’s a special kind of alchemy that can be found when relatives share the screen. Children, parents, siblings, whatever the case may be, the familial bond is clearly evident. In the case of “Stella’s Last Weekend,” all of that applies. Writer/director/co-star Polly Draper has employed much of her family here. In particular, she has her sons Alex Wolff and Nat Wolff playing siblings and her onscreen children. This results in a feeling of easiness that can’t be faked. Even as other moments in this film turn cliched, the chemistry between the three always rings true. Hell, even the dog here is the family’s actual pet!

Without this unique bit of casting, Draper’s movie would have felt a little too slight. Much of the pleasure found here is in seeing the Wolff boys play off each other. Whether it’s the two of them, or either of them with Draper, or especially all three, the sparks fly. Instead of a bickering family, they’re a joking/wisecracking one, and it feels real. While this is clearly fiction, it wouldn’t be surprising at all to discover that many parts of “Stella’s Last Weekend” evolved out of real life. It has the conversational feel of authenticity.

Oliver (Alex Wolff) and Jack (Nat Wolff) are brothers and best friends. Oliver is still in high school in Queens, while Jack has left for college. When Jack returns home, they pick up like nothing has changed. This time, however, there’s a sad occasion for his return. Jack is there to help the family say goodbye to their elderly dog Stella. Their single mother Sally (Draper) has arranged a party to celebrate her life before she’s put down. They all call attention to its oddness, but the family, on the whole, is odd, so it’s par for the course. When the brothers aren’t goofing around, they’re making fun of Sally’s boyfriend Ron (Nick Sandow), who is hopelessly uncool.

Things take a turn when Oliver tells Jack about his new girlfriend. He’s, of course, happy for his brother, but then he meets the girl that Oliver is smitten with. It’s Violet (Paulina Singer), the girl who previously broke Jack’s heart. Oliver is completely unaware and wants the three of them to spend time together. That close proximity leads to some awkward situations, especially as Violet begins falling for them both. All the while, Stella’s party and final moments await. For what it’s worth, despite the morbid sound of this, it’s largely a very humorous film.

This is a perfect vehicle for both of the Wolff boys. “Stella’s Last Weekend” showcases more charm than we’ve seen yet from Alex, while Nat gets to play an older and sadder character than usual. The movie lives and dies on your enjoyment of their company. Luckily, they’re a hoot. There’s some sort of special blend that lets them feed off of each other terrifically. Alex already wowed earlier this year with “Hereditary,” while Nat has been underrated for some time now. He has the higher profile, due to “The Fault in Our Stars,” for example, but together they’re a force.

The chemistry also extends to the boys’ scenes with Polly Draper. Any scene where the three of them are just riffing is a blast, especially if Nick Sandow’s Ron is exasperated at the same time. The three of them are best in show, as Paulina Singer is a bit underdeveloped as a romantic pairing. Singer is fine, but just not as memorable. The same goes for Sandow. Draper and the Wolff gentlemen make this one what it ultimately is.

Polly Draper is not just a solid actress, but an effective filmmaker as well. “Stella’s Last Weekend” is well-paced and often clever. Her direction focuses on the dialogue and looks at her children with a quiet admiration. Her script is full of funny lines, though in the third act it veers toward a lot of cliches. Luckily, Draper finds a way to make the impending death of a dog, not a complete heartbreaker. She even makes the behind-the-scenes aspect a family affair as well, with Michael Wolff on hand doing the music. They all must be very proud of the final product.

Fear not dog lovers, “Stella’s Last Weekend” won’t bring you to tears. Surrounding a love triangle with this animal subplot was tricky, but Draper pulled it off. The Draper/Wolff family came to play, with their infectious spirit rubbing off on the whole product. This easily could have been little more than a vanity project. Instead, the film is a charmer with a lot going for it. If you seek this movie out, it will almost certainly bring a smile to your face.

“STELLA’S LAST WEEKEND” IS DISTRIBUTED BY COLUMBIA PALADIN AND OPENS IN THEATERS ON OCT. 12.

GRADE: (★★★)