"You are my friends, if you do the things that I command you." Surely friendship implies partnership and not the hierarchical relationship implied by issuing commands. So issuing commands is not appropriate, because it suggests that the friendship will be at least threatened if one does not obey. That's not compatible with friendship. So obedience is also not appropriate. (I'm not commenting on the significance of the context of your quote.)
I would think that a partnership is one form of a "union of wills". It certainly implies concord, if that means harmony, not conflict.
Aristotle says in the NE that a friend is another self. Quite what this means is not really clear and the question of translation complicates matters. But can one issue commands to oneself? In a sense, yes, but, just because they are issued to oneself, they are more like exhortations than commands. I suggest that applies also to another self.
I'm assuming that a command implies a hierarchical relationship, in which disobedience is followed by some form of punishment. That's certainly not compatible with friendship.