Earl Cave’s first onscreen appearance was in the 2014 music documentary 20,000 Days on Earth: Earl and his twin, Arthur, are sitting at home in school uniform either side of their father, the musician Nick Cave. All three are eating pizza and watching Scarface. The boys are 13.

“Films were a huge part of my childhood,” says Cave. “Inappropriate movie night was once a week and my dad would show us ungodly, outrageous films. We were obsessed with getting as scared as possible.

“We weren’t interested in the acting or directing. It was just: ‘Fuck, let’s get the goriest film. Put on Chucky 3 and eat some popcorn.’”

Cave is now 19, lean and long haired, with big eyes. When he gently gesticulates with his ringed fingers, the resemblance to his father is impossible to deny.

Next month, Cave will be on screen as other people in two films. True History of the Kelly Gang is a bloody jaunt across 19th-century Australia with notorious bushranger Ned Kelly, directed by Justin Kurzel (Snowtown, Macbeth). Days of the Bagnold Summer, meanwhile, is an adaptation by Simon Bird (The Inbetweeners, Friday Night Dinner) of a graphic novel about domestic ennui in Bromley.

He has not been acting long, but his turns so far have been striking. His role as Frodo, the hyperactive petrol station attendant in The End of the F***ing World, prompted BuzzFeed articles, fan videos and endless memes. “People were calling themselves Fro-hos,” says Cave. “Apparently I was the Fro-daddy. It was surreal.”

As Daniel – brother of Ned – Kelly, Cave careers through the outback plastered in warpaint, wielding a gun and wearing a full-length wedding gown. The film is a punk rock spin on the outlaw’s story and as a bonding exercise for the cast, Kurzel even had them form a band.

“He totally sprung it on us,” says Cave. “We turned up for pre-production and he said: ‘You’re starting a band, we’ve booked you a gig, go and write songs.’” It worked, though: “The idea of us against the world, sticking together and if anyone gets in our way then fuck ’em.” The makeshift band’s tunes feature on the soundtrack, and an album of ramshackle garage folk-punk is potentially on the cards. Still, says Cave, they were “kind of shit. We didn’t have much time, we just bashed it out; my bass sounds dreadful.”

In Bagnold Summer, meanwhile, he is a sullen grump with an all-black wardrobe and Metallica attached to his ears. It is a more subtle and low-key performance, steeped in hormonal stubbornness, to which Cave brings surprising tenderness and grace.

“I can do angsty teenager and wild teenager,” he grins. Was he either? “I was pretty pleasant. I think I was a bit of a dickhead around 15; I started to dress horrendously. I’d wear leggings, spray-on jeans, and then sag them around my backside.”

If your parents are as immaculate as Nick and his fashion designer wife, Susie, baggy bottoms evidently count as extraordinary rebellion.

“I now feel sorry for them having to walk around with me,” he says. “They let me do my thing but were like: ‘Maybe you should try a straight leg?’ And I’d be like: ‘Fuck off, dad, I don’t want to wear a three-piece suit!’”

Outlaw blues … Earl in a still from True History of the Kelly Gang.

Cave grins at the memory of his teenage sartorial wobbles. But the truth is, during his teenage years, the whole Cave family were faced with an unimaginable tragedy: the death of Earl’s twin, Arthur, aged 15, who fell off a cliff having taken LSD. In the 2016 documentary One More Time With Feeling – Cave’s second screen credit – director Andrew Dominik returns to the household, this time finding it crippled by grief.

“Andrew is a family friend, so it didn’t feel intrusive but he did crack into us a bit,” says Cave. “He left me out as he knew I was under a lot of stress. I had a lot of shit going on; I had my fucking exams in the middle of all that.”

Cave’s brief appearance comes when he visits his father in a recording studio, gently running his fingers through his mother’s hair before the three of them embrace. Despite the film’s rawness, Cave is thankful for it. “It didn’t feel invasive and I don’t know how the hell Andrew did that. It was a beautiful tribute to Arthur.”

Cave is hesitant to discuss his twin too much. Photos of the flowers and handwritten note he left at the accident site were shared online, paparazzi were at the inquest, with the media insinuating a lack of parental responsibility from his father.

“What happened really changed me,” he says after a pause. “It matured me very quickly at an early age, especially emotionally.

“The intense time that I spent with my family, and with all of us nourishing each other, meant we came out of this with a greater knowledge of what it’s like to lose someone. We’ve all come out as very different people but I actually think for the better, which is a difficult thing to say.”

They are an especially close – and open – unit. Love heart emojis from his mother fill the comment sections on Cave’s Instagram. One photograph of his dad is captioned: “To the blood-sucking nightcrawler of East Sussex. I love you unconditionally.”

Both his parents have explored the grieving process through writing: his father with music and answering fan mail, his mother on her website, the Vampire’s Wife. “They have found their outlets,” says Cave. “These are things that keep you busy and focused but are also a means of answering other people’s questions in a way that answers some questions you might have for yourself.

“Film has been really important to me for that,” he says. “I’m doing all of this for Arthur. I want to make something beautiful out of something tragic.”

True History of the Kelly Gang is released on 28 February in the UK, and is streaming on Stan in Australia; Days of the Bagnold Summer screens 4 and 5 March at Glasgow Film Festival