I don't think Shrei knows that, actually.
I know he does. It’s impossible for a person like him or anyone of nobility to be ignorant of the status of the people around them. Especially if it’s directly related to them becoming family. Especially for someone curious and with means to investigate
Has it been stated in the story that Shrei knows her true identity? Because it seemed like he had no idea about her curse when he was talking to their adoptive father about her. And the reason why I think he doesn't know is the way he's reacting to her (and what his adoptive father muttered about the failed cure). I don't doubt that your pint of view is a common sense way of thinking, but Shrei's reactions just speak to me that he is not fully knowledgeable about our MC.
*point
Gosh, I hate that we can't edit comments in replies.
I love that all of them are instinctively falling for her baby charms despite them knowing she's a fully grown woman on the inside.