Humble Bundle Steam + Origin Multiplayer?

i think both got same multiplayer servers , so origin players can play with steam players

Yes

You can use the steam key, then give your Origin key to your friend... steam will give you a different key to access MP for your games... so yes, you can use the steam key, steam gives you a key to put in your Origin, to access MP for that game, then you give your friend your Origin key from the bundle (NOT the one provided by steam), he activates it, and then you can play :)