that's it!

Hi Ivon!
There are TWO ways to address the person who has birthday.
If it's a good/close friend of you:

Herzlichen Glueckwunsch zum Geburtstag wuenschen Dir
Ivon und Heather
***************
If you want to put it a bit more formal you can say:

Herzlichen Glückwunsch zum Geburtstag wuenschen Ihnen
Ivon und Heather

I assume that you want to write a birthday card or smth like that. If you also want to mention Hans' name (which is not really necessary in German) you can either write it on the envelope or simply put: Lieber Hans! (means: Dear Hans!)...Herzlichen Glueckwunsch.....

by the way: if you really want to be correct you have to write "Glueckwunsch" and "wuenschen" with u-umlaut (u with two dots above --> "ü" ....I don't know if you can read it here:-)....but with handwriting it shouldn't be a problem.
Hope I could help you ;-)

*dir* if he's a close friend of you *Ihnen* is more formal.