Why did Yakov refer to Lavan as "Lavan ben Nachor" and not 'Lavan ben Besu'el'?
Ramban #1: Because Nachor, the head of the family, was more important than Besu'el. 1
Ramban #2: It is also possible that Besu'el was a nonentity, and Lavan did want people to attach him to him, only to his grandfather Nachor. 2
Ramban #3: It may also be that the Torah mentions Nachor, who was the head of the family, in honor of Avraham, whose brother he was.
Moshav Zekenim: It is because the city was called "Ir Nachor."
Yakov could not mention Besu'el's name without calling him "my grandfather 3 " or a title of respect. He did not want to do so, for he was an idolater. (PF)
As we find later in Vayeitzei, where Lavan himself referred to "the G-d of Avraham and the god of Nachor". See also Oznayim la'Torah, who brings other proofs as evidnce of Besuel's importance.
We find (in Bereishis 24:50) "And Lavan and Besu'el answered (Lavan did not esteem his father, and spoke up before him).
It is clear from Kerem Shlomo (8:8 p.8, cited in Daf Al ha'Daf Shabbos 33b) that this is forbidden. I did not find anyone who forbids doing so for a great grandfather.