First of all, don't use nickname, just use party1 - it will be always your teammate in 2v2.
Secondly - there is no need to use two /cast commands or split them like you tried to.
Here's my macro for Rejuv:
/cast [mod:alt, @mouseover, help][mod:alt, @target, help][mod:alt, @party1, help][@player] Rejuvenation
If I hold Alt modifier key - it will first attempt to cast it on mouseover, if there is any, and if not - it will cast on target. If there is no modifier key pressed - it will cast on myself.
I don't use "exists", try to drop it too, like this:
/cast [@mouseover, help][@player] Rejuvenation
It works for me as it supposed to - if there is mouseover - it heals mouseover, if not - it heals myself.
I'm not sure though what you're trying to achieve with this macro, because during 2v2 game it will never heal you, it will just heal your friend, no matter what.
If you want to make this macro heal yourself when your hero is dead then you can also use "nodead" flag, then if party1 (your friend Munir) will be alive - it will heal him, if not - it will heal you:
/cast [@party1,help,nodead][@player] Rejuvenation
But I still think this one is pretty useless, because you often want to apply Rejuv on yourself and on your teammate.