Responses
Shouhei is still living with his parents and brothers, so officially - Shizuma haven’t met Mito as the ‘owner’ where Shouhei works.
The parents and brother met Mito when Shouhei was about to live together with Mito :)
The timeline or my clue was Shouhei is still in the house. :)
Hope that clears things up.

Doesn't Shizuma know what his brother's boyfriend looks like? And does the brother know that that's his boyfriend's brother?
I'm so confused ლ(´ڡ`ლ)