Deobandi by definition means those who endorse the four elders of deobandism or those who hold them in high esteem. So they should be kafir. Does a regular muslim endorse four deobandis ? Is a regular muslim called Deobandi ? NO Deobandi is specific to those who approve 4 elders of Deobandism. Please read https://archive.org/details/HussamUlHaramainEnglish Husamul Haramain (Ḥusām al-Haramayn) or Husam al Harmain (The Sword of the Two Holy Mosques) 1906
No. Unless he is kafir for other reasons. No ruling on him. Ruling is only for those who agree with the passages.
If a person grew up in a deobandi family but dont know about the 4 then can they be ruled as kafir? If a person wholeheartedly believes that his akabrin did not say the words of gustakhi then what is ruling on him?