Gabriel-
It's no problem for these codes to appear in other sections of the page. There are many character sets out there, and what may appear great to you (without codes) looks like gibberish to someone else. The codes help make for a uniform experience for everyone. For instance, there are no "smart quote" keys on your keyboard, yet some programs (like Word) will automatically insert these for you. To have these on a web page most systems will convert these to codes for you. The ampersand, however, falls into this category since it's often an escape character for other characters.
So, the place we're still really most concerned about is the meta title. I'm not sure why the mb_convert_encoding() function didn't work for you?
If you'd like me to take a closer look feel free to message me. This is solvable - I've done it before on WP sites.