What does "h m h m" mean?
 

And what does this mean: りょうかい

Both from Koebu.

りょうかい is word someone uses after receiving orders or instructions meaning "Roger" or "Check" or "Yes, sir", usually as 了解しました or 了解です.

and "h m h m" is either a sound of someone clearing his throat, or the japanese "hmm" that anounces acknowledgement of whatever someone said, used as "I see, I see", "aha", "right...", etc. Though mind you, if we don't have this "h m h m" in context it can even be a sound of an almost starting car engine on a winter day.

"hmhm" comes from ふむふむ, which is what we say in casual speech to mean roughly "I get it.", "Oh, I see.", etc.

Your dictinary should have ふむ if not ふむふむ.