I can't believe I need to explain this, but no, "one in the same" is not a correct usage, it's a mistake. No, it doesn't mean something subtly different. It doesn't mean anything. You heard the phrase wrong and didn't think about the component words and how they would make grammatical sense.
https://www.quora.com/Which-is-corre...ne-in-the-same
"One in the same" is an eggcorn:
https://grammarist.com/usage/one-in-the-same/
An eggcorn is... well I'll give you a definition of that phrase because you probably don't know it:
"Eggcorn" is a mishearing of "acorn", that's where the word comes from. The idea is that someone who doesn't know how to spell "acorn" mishears "eggcorn", and assumes this makes sense because an acorn kind of looks like an egg and/or kernel of corn, ie egg-corn.
Kind of like how you've misheard "one and the same" as "one in the same" (which is easy to do, because "and" and "in" often reduce to the unstressed pronunciation "ən" in common speech due to being short syllables - this is why you sometimes see "and" spelled "'n"), and you've assumed they're different things.
P.S. I only speak one language, my native tongue. I repeat, learn the freaking language.