Let's assume i have two same PS ships with both Attanni Mindlink + Glitterstim. How many stress tokens both ships get if they both use Glitterstim?

You choose which of your ships uses Glitterstim first (regardless of PS).

Whichever ship does it first receives one stress, then anyone they're Mindlinked with will receive a stress (unless they're already stressed).

Then, if one of the other ships with Mindlink uses Glitterstim, that ship will get another stress, none of the other Mindlinked ships will because they already have at least one.

So assuming none of your Mindlinked ships start out stressed, the first one to use Glitterstim will have one stress, any others that use it will have two.