I have searched multple sites and have not seen anything saying that this is not possible.
Seeing as both Pokemon are treated as separate Pokemon, as in they are not copies of one another, I'm going to say Yes this is possible for both scenario (facing 2 Shinies or 1 Shiny and one regular).
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NOTE: Don't be fooled by YouTube videos that show this. They can easily be hacked, no matter what they say.