Is it considered disobedience if one goes against their parents' wishes in choosing a college, where he desires to study Law while they want him to study Veterinary Medicine, knowing that he finds no guidance in the Istikhara prayer?

Obeying and honoring one's parents is obligatory unless it involves disobedience to Allah or causes harm to the individual. This is based on the Prophet's (peace be upon him) saying: "May his nose be rubbed in dust (i.e., may he be humiliated) who found his parents, one or both, in old age, but did not enter Paradise." And also his saying: "Obedience is only in what is good," and "There shall be no harm or reciprocating harm." Seeking guidance (Istikhara) is a recommended act of worship before every matter. It is a sign of a person's felicity to seek Allah's guidance and be content with His decree, and a sign of their misery to neglect Istikhara and be displeased with what Allah has decreed. Therefore, whoever performs Istikhara must be content with what Allah decrees.