When Hudson Fasching speaks to his brother, Cooper, it is on the speakerphone with his mom.

That is, he says, better than FaceTime, because Cooper’s eyesight is poor.

“He really likes the audio and likes to hear my voice,” Fasching told The Post. “Mostly rubbing his chest and playing with him a little bit like that, so it’s the easiest way to communicate with him.”

Cooper suffers from a mitochondrial disorder and is unable to walk or talk, requiring constant care.

The disorder, infinitesimally rare, struck the family a second time when Hudson’s sister, Mallory, was born a year after Cooper.

Hudson, the oldest, grew up not just as a high-profile hockey player but as one of Cooper and Mallory’s caregivers, along with his parents and hired help.

“It’s definitely not a traditional childhood, I guess, in terms of playing with your brother and sister,” he said. “But it was good. I still enjoyed spending time with them. I felt a lot of responsibility as the only brother to do my part to try and take care of them.

“I loved my childhood, obviously. They’re my siblings and I love them, obviously. It definitely made my relationship with my parents a lot tighter. Cause we were spending quite a bit of time together, just out of necessity.”

One of the cruelties inflicted by the disease is an all-too-short life span, with victims expected to live until their late teens or early 20s.

Cooper, a year and a half older than his sister, is doing “as well as he can be doing,” Hudson said, and has outlived his life expectancy.

Mallory died last September, at 23, when Hudson was in training camp with the Islanders.

At that training camp, Hudson was an unknown, trying to make the Islanders after a few years shuttling between the NHL and AHL with the Coyotes.

He was assigned to AHL Bridgeport out of camp, called up to the Islanders in December and never left, becoming a lineup mainstay and signing a two-year NHL deal that was announced on the first day of the offseason.

That came nearly 10 years after Fasching was drafted by the Kings in the fourth round and seven years after he made his NHL debut with the Sabres.

When he left his family at 16 years old, joining the U.S. National Team Development Program, he did so knowing the NHL was the goal.

“It took me quite a long time to make that decision,” Fasching said. “Obviously weighing leaving family and such. And eventually it was — at some point, I knew I was gonna have to leave and I knew this was an incredible opportunity to represent my country and go play in Europe, go play all those teams, develop, play with the best players in the country. Get coaching, competition, the strength coaching and get outside the Minnesota bubble, too.

“As much as it was a close family unit and we did spend a lot of time together, it kind of ends up forming a little bit of a bubble for myself. I wanted to get outside and explore that a little bit.”

No one could have known how long it would take for Hudson to catch on in the NHL.

But more than anyone, he has the perspective to understand what’s important and appreciate what he has.

His family is a motivation to do more, to keep going.

It has paid off.

“He definitely has something special. He’s earned it,” Jean-Gabriel Pageau, Fasching’s linemate, told The Post. “He’s worked so hard all of his life. Through family stuff, through fighting injuries or anything, he’s battled all that out and come in and showed that he has a place in the NHL.”

For the first time since 2016, Fasching is on the opening night roster for an NHL team.

For the first time ever, he is likely to be in the lineup every night.

It is rare that his family can come to see him play, and Hudson thinks the last time Cooper did so was when he was in college at the University of Minnesota.

He is grateful all the same.

“I think it’s given me perspective, even from a young age, of just gratitude,” Fasching said. “Just be grateful for everything you can do and try to do everything to the max ability that you can, because there are other alternatives to life. I was obviously very close to being them.

“And so it’s definitely a daily reminder of that and I think that’s always been the biggest thing for me. Recognizing what you have and trying to make the most of it.”