I will return to this when I'm not on my phone (and a bit sangria tipsy)

BUT
The Greybacks - Merida Greyback and Murdock Greyback would be likely buds!

Merida would definetly have been interested in gaining some skills in Field medicine and have been interested to learn from him - either before or after his time at the hospital.

He would know Murdock from ministry, who also could have introduced him to Merida.

I don't have many other MC - but I could also see Luna Wakefield freaking him out, but asking for uncomfortable level of detail about field injuries....'for research'