Good question!

Only Jesus is ever called "the Son of God" in the Bible.

Some people think Adam is called "the son of God" in Luke 3, yet that's only due to a bad translation. The original language, Greek, only says Adam is "of God." Translators add in the words "the son," which aren't in the original language.

Israel is called "My son," but that is quite a different phrase than being called "the Son of God."

As for Psalm 2:7, that's a Psalm prophesying about Jesus -- that He is the Son of the Father. Hebrews 1 quotes this verse as part of its proof that Jesus is the Son of God.