I'm not an admin, however I can probably echo what one might say to you.
"Sharing/distributing Personal Information [including Passwords] is strictly against the rules and terms of service"
Meaning, both you and your friend may get banned because you both are violating the known and highlighted rule. Things can especially get sketchy if dishonesty ensues and something happens to that account.
If you intend of assisting, you can use your account and aid him while he play his.
But, if you insists on the method your friend suggested and you two have deep trust for each other, well, I won't say to go ahead and do it, what I will say is that, bear in mind the rules.
Helping out friends is encouraged in this game! It's one of the reasons Wizard101 and Pirate101 are great games! The fact that you can ask anyone for help and become friends with anyone.
Anyways, as long as you aren't violating the terms of service (which you agreed to upon installing the game) then you are fine. The only way you could get in trouble is if you were to break the rules in game... then we got a problem. I hoped this helped at all
Peace out wizards of the spiral Ethan Griffinthorn Lvl 78