Is wiping over the khuffs (leather socks) simultaneously obligatory or merely preferable, and must one wipe the right foot with the right hand and the left foot with the left hand?

It is sunnah when wiping over the khuffayn (leather socks) to wipe them simultaneously by placing the hands with fingers spread at the tips of the toes and then passing them up to the shins once. It is not obligatory to start with the right, but the difference in this regard is about what is better. Any method of wiping the top of the khuff suffices, and it does not matter if one wipes the right first then the left, or if one wipes the right with the left hand, except that the sunnah is to wipe each foot with its respective hand.