Matthew, 18, has featured alongside his sibling for the under-23s this term, playing together in central midfield before Sean's progression into the senior squad.
Since making his full Premier League debut at Chelsea, Sean has enjoyed a whirlwind start to 2019, netting his first goal for Newcastle in a 4-2 Emirates FA Cup victory at Blackburn Rovers along with starring in a memorable 2-1 win against Manchester City, testing himself against the Premier League champions' high-profile midfielders.
Last season, the Academy graduate featured for League One Blackpool on loan, which Matthew feels was beneficial for the 21-year-old in his successful rise through the ranks, and he believes his brother has fully deserved his opportunity in showcasing his talent on the biggest stage of English football.
"I've been very impressed with Sean's performances lately," Matthew told nufc.co.uk. "A year ago, he was playing at Blackpool in League One and I think that did him the world of good going there to get experience before coming back.
"I think he has shown his class and how good he is. Once he's got into the Newcastle side, he hasn't just done a job but I think he's been one of their best players. He was awarded man of the match against Wolves and has already played against many of the best midfielders in the Premier League. He hasn't been out of place one bit and they have picked up results with him in the team which will only be good for him.
"For his age, I think he's quite mature. He knows his role and whatever the manager tells him, he goes out and does well, showing his consistency in the last seven games and that he can perform at the highest level on a regular basis."
The duo, born in North Shields, both played for North Shields Juniors before linking up at Newcastle's Academy, with Matthew revealing his appreciation for his older brother's helpful qualities whilst playing together.
A spectator at Anfield for Sean's top-flight debut against Liverpool on Boxing Day, Longstaff also recalled the moment he witnessed his brother being brought on from the bench to make his Premier League bow, followed by a chorus of chants from the Geordie supporters.
"He makes the game easy when you play with him," Longstaff added. "He is an intelligent player and helps to find the ball for you as well as himself. I love playing with him. My parents and grandparents like to watch the both of us play together and hopefully it can happen again in the future but it was great playing alongside him at the start of the season.
"I remember going down to Liverpool to watch Newcastle play and it was a bit of a surreal moment when you see him coming onto the pitch and you hear chants sung about him. It's a bit mental when you listen to it as he's the same person that you are having a laugh and joke with in the house the night before. It's great for him and I hope he can do it for many more years. He deserves everything he is getting for how well he is playing."
Following Sean's positive performances, the Academy graduate has inspired his younger sibling to follow in his footsteps to play for his boyhood club.
The last time a pair of brothers featured for Newcastle United in the same match was back in 2011, with Shola and Sammy Ameobi starring together in a 2-2 draw at Chelsea.
Longstaff said: "I'll always ask him questions and he'll always help me out with little scenarios in the game. Being around him when growing up, and knowing he's managed to get that opportunity, it gives you hope that another Geordie lad can get into the first team.
"It would be a dream for me to play with him in midfield one day for Newcastle United but, for now, I'll have to keep working hard and see what happens.
"It gives other people around the Academy a bit of a buzz to think you can go out and do what he is currently doing. Everyone is very happy for him and people have been talking about his performance at Wolves, which is a great thing to hear about your brother but it also gives players the extra determination to try and reach the top level."
