Honestly, I would call them both up and sooner rather than later.
Yoho isn't being challenged at all in the minors. He's ready for the show and probably ready to dominate. Might as well start getting ready for life without Devin of which he will be a key part.
As for Mis, they look committed at this point to pitching him out of the bullpen for the remainder of the season to limit his innings. He's mowed down AAA hitters his last two appearances and hasn't issued any free passes. If he keeps that up over the rest of the month, I think you absolutely have to give him the call. Yes, he doesn't have to be added to the 40 man until next offseason, but let's be honest: do you really think he won't already force himself onto the 40 man before then?
Bottom line is we're going to need arms who are capable of getting outs in the postseason. We're almost certainly not going to get as many out of our rotation as in past years, which means more are going to have to come from the bullpen. With Hudson, Koenig, etc. experiencing declining results as a consequence of heavy early season usage, Yoho and Mis can step in to steady the ship. Because their arms are the definition of postseason caliber.