I'm pretty sure you're talking about 'The Bartimaeus Trilogy' by Jonathan Stroud. Nathaniel is like an orphan since he gets taken to become a wizard apprentice and there is a bunch of magical artifacts in the books, particularly the Amulet of Samarkand. Plus, his relationship with Bartimaeus and Kitty kinda forms a trio. It's a bit of a shot in the dark but could be it!

You might be thinking of 'The Chronicles of Prydain' by Lloyd Alexander. The main character, Taran, isn't exactly an orphan but he's an Assistant Pig-Keeper with unknown parents, which is basically orphan-adjacent. His companions aren't quite a trio but there's a collection of friends that could feel that way. And there’s a magical artifact called the Black Cauldron. It's old school, but a pretty solid series.

Is it possibly 'The Tapestry' series by Henry H. Neff? The Hound of Rowan is the first book. It's got that young orphan type, Max McDaniels, who's magic and gets sent to this hidden school for the gifted. He’s got two close friends and later on they have to find this magical artifact. It's a bit of a deep cut but it ticks some of your boxes.

That's def Harry Potter, you sure you're not just misremembering? LOL maybe you slipped through the cracks of the wizarding world and they wiped your memory. Rip.

idk about a specific book but this kinda sounds like every fantasy series ever? magical schools and orphans are like bread and butter of fantasy lol

Man, this is taking me back. Could it be the 'Circle of Magic' series by Tamora Pierce? Main character's not a boy though, and it’s about four friends, each with their own unique magical talent. They're not orphans but kinda outcasts? Been a while since I read it but it was good stuff.

What you're describing sounds a lot like 'The Magicians' trilogy by Lev Grossman. Quentin Coldwater is the protagonist, who discovers that he has magical abilities and attends a college of magic in New York. Not exactly a magical 'stone,' but they do have magical artifacts and there's a big emphasis on both friendship and the disillusionment with the fantasy world of Fillory, which is kind of similar to Narnia. Definitely not for kids though, it's got darker themes.

Hmm sounds kinda familiar, maybe The Magicians by Lev Grossman? There's a magic school called Brakebills and the main character Quentin is pretty messed up. Not exactly the same, but maybe?