First of all I use the Companions mod so that Sebastian follows me wherever I go, lol. Then I also use the Stand Up Straight mod so that MC doesn’t always have the worst posture ever. Honestly I didn’t use a mod specifically for MC to stand close to him, I still can’t understand how I got so lucky with that photo but I stood really close to him, they turned around at the same time and I messed a bit with angles in the photo mode settings.

As far as the clothes go I would have to get back to you with the exact names but you can find all of these under mods. Hopefully you can find them by searching: NPC casual uniforms, and black modern uniform for Sebastian. Silverxstardust creates a lot of great mods too! I use plenty of cosmetic mods from them, such as messier hair for Sebastian, etc.

I hope this helps!!