So which heresy is the Mormon one where God has a wife and a father and probably brothers and sisters etc leading to infinite Gods? This is a serious question because I have a son who likes a Mormon girl. This Mormon heresy includes that Gods are created, that men become Gods and that Jesus and Satan are brothers. What a mess!!
Where to begin? :)
You spotted the main one. Who God is, who Jesus is.. Heretical Christology.
Mormon heresy is an odd, unique mix. Here’s a brief list of early heresies and you can see pieces of LDS in some:
http://www.ignatiusinsight.com/features2005/kwhthd_ancntheresies_july05.asp
I don’t know your or his religious background, but I think what you could do is look at the basic theology of Christians - Catholic and Protestant. There are some main areas of agreement on very basic absolute beliefs.
Then contrast LDS’s basics with these. I think to a thinking person the variance would be striking.
Of course, there’s a woman involved so your son might not qualify as ‘thinking’ right now..
:)