Episcopalians, Seventh day adventists , Baptists , Methodists all beleive the same on the Trinity.basically. God is Father Son and Holy Spirit ;that make up one God. Three persons make up one god. All have allways existed.
The incarnation is when Jesus or God the Son came to earth in th eform of a human. Jesus was fully god and fully man the scriptures can speak of Jesus a man and Jesus the son of God. Jesus has two natures.
When I was a young boy I went to a bible study group in the SDA church and we went throught the statement of beleif of the Episcopalian church and beleive it or not it is the same as what SDAs beleive on the Trinity as well as every other beleif. Of course the SDAs have a few extra beleifs that are not included in the Westminister confession