I think, in ecclesiastical contexts the first - "Im Namen Jesu Christi" - is the standard phrase. From a grammatical point of view "Im Namen von Jesus Christus" would be correct as well. But using this variant would show that you are not familiar with the church's tradition to use the latin Genitiv for the name of their Saviour, or it would suggest that you are not willing to submit yourself to the standard phrase, maybe indicating a distance to the church.
"In den Namen von Jesus Christus" is a wrong translation of "In the name of Jesus Christ", because it uses Akkusativ instead of Dativ - it would be translated to english with "Into the name of Jesus Christ"
"Im Namen Jesus Christus" is wrong, since - according to http://www.duden.de/rechtschreibung/Jesus - "Jesus Christus" is not a valid Genitiv of "Jesus Christus"
The latin declination of "Jesus Christus" seems exceptional in german grammar, normally the declination of foreign words follows german rules, with the exception of Nominativ Plural of some latin and a few greek words, which are sometimes declined after latin or greek schema (for instance: "Lexika" as plural of "Lexikon"). For this topic also see Seit wann werden lateinische Wörter im Deutschen nicht mehr lateinisch flektiert?
The specialty of "Jesus Christ" in this question reminds me to the latin word iovis ("jupiter") who has had a whole own declination. That's why I guess that the latin Genitiv used for Jesus Christ in ecclesiastical contexts has the function to express the speciality of the name of their god. Even if this was not the intent of the exceptional declination, this is the effect - at least to me.