The Prophet (peace be upon him) said, "Praying in congregation is twenty seven five times more meritorious than praying individually." (Reported by Bukhari on the authority of Abu Sa'id al-Khudri).

So, there is no reason for you to miss the opportunity for gaining the extra rewards by praying with your wife. When you are leading, she should stay behind you; there is no hard and fast on where she stands behind you; the only thing is you should be standing close enough for you to have any physical contacts, during the prayer.