Were Alma and Mormon direct descendants of Nephi?
Answer: Alma and Mormon were both direct descendants of Nephi.
“And Helaman was the son of Helaman, who was the son of Alma, who was the son of Alma, being a descendant of Nephi who was the son of Lehi, who came out of Jerusalem in the first year of the reign of Zedekiah, the king of Judah.” (Introduction to 3rd Nephi)
“And I, Mormon, being a descendant of Nephi, (and my father’s name was Mormon) I remembered the things which Ammaron commanded me.” (Mormon 1:5)
Source: Book of Mormon