Are these sentences grammatically correct? They are translated from Thai song lyrics.
Whose sunshine do you belong to? Who is your sunflower?
Based on the literal translation from Thai that you provided in comments, and on the normal interaction between sunshine and sunflowers, the sentence is grammatically correct but fails to convey the intention.
The word “of” in your literal translation doesn’t mean you belong to that person’s sunshine, but that you are the provider of the sunshine to the unnamed “who”.
Try this as a translation: “Who are you shining on? Who is your sunflower?”