Here "they" refers to the unclean spirits. It is they who are causing the people they possess to do things. This can be made explicit. Alternate translation: "they caused the people they were possessing to fall down before him and to cry out to him" (See: [[rc://en/ta/man/translate/figs-explicit]])
The unclean spirits did not fall down before Jesus because they loved him or wanted to worship him. They fell down before him because they were afraid of him.
# You are the Son of God
Jesus has power over unclean spirits because he is the "Son of God."
# Son of God
This is an important title for Jesus. (See: [[rc://en/ta/man/translate/guidelines-sonofgodprinciples]])