At level 9, the Rogue's Phantom subclass (Tasha's Cauldron of Everything) gets the 'Tokens of the Departed' feature, allowing them to create 'soul trinkets'
When a life ends in your presence, you’re able to snatch a token from the departing soul, a sliver of its life essence that takes physical form: as a reaction when a creature you can see dies within 30 feet of you, you can open your free hand and cause a Tiny trinket to appear there, a soul trinket.
These trinkets have a couple of uses, one being:
While a soul trinket is on your person, you have advantage on death saving throws and Constitution saving throws, for your vitality is enhanced by the life essence within the object.
Given that you can have more than one soul trinket at a time (up to your proficiency bonus), it's tempting to pass them around. It's unclear whether the quoted soul trinket benefit is a property of the trinket or of the rogue, and hence unclear whether another character holding a trinket would gain advantage on death and Constitution saving throws.
Best Answer
"You" and "your" refer to a phantom rogue having this class feature.
The Tokens of the Departed feature says, as you have quoted:
This "you" can only refer to a phantom rogue having this class feature. If your friends are also phantom rogues, then they should be able to use your soul trinkets. Otherwise, they lack the class feature that allows them to use the soul trinkets.
Compare this to the Chronurgy Wizard's Arcane Abeyance feature:
This feature does not say "while you are holding the bead", rather more generally specifies "a creature holding the bead" - a bead created with Arcane Abeyance can be given to another creature for use.
The Transutation Wizard's Transmuter Stone feature goes even further out of its way to clarify that another creature can make use of the stone:
It doesn't get more explicit than that. The trend seems to be that when a subclass has a unique bauble with some features associated with it, the rules are going to tell you it is usable by others, which means the default is probably that it isn't.
To put it another way, the Phantom Rogue has this feature, and this feature says:
It stands to reason then that the following is true for a character without this class feature:
A creature without this class feature may not be able to hold them at all.
What I'm about to tell you is probably an accurate rules as written ruling, but probably departs from what makes sense. There is an important statement in the feature description that may prevent other characters from holding the trinkets at all:
Since non-(Phantom Rogues) do not have this class feature, it seems that they would not be able to have any soul trinkets, since it is this class feature which give the Phantom rogue the ability to have a number of them equal to their proficiency bonus. But like I said, while this is RAW, it seems a bit strange.
This raises some questions.
There are some statements in the Tokens of the Departed description that do raise some questions, in light of the ruling I made above. In particular, we see:
This third bullet begs the question, "why would the soul trinket be located somewhere else?"
It seems to me that in the first two bullets "on your person" is there only to distinguish between having one or more soul trinkets and not having any at all, without implying that you can give them away.
The third bullet is more difficult to nail down - if there's no reason to give them away, why would they be located somewhere else?
This statement is there to preclude concerns about the action economy of object interaction.
The statement "no matter where it's located" is there to clarify that I don't have to holding my soul trinket to destroy it. I don't have to use my object interaction to draw the soul trinket from my pack into my hand before using my action to destroy it, nor does destroying it require a free hand.