In I Kings 15:1-2 and I Kings 15:9-10, both Abijam and Asa are said to be sons of Maacha the daughter of Abishalom. Does that mean they are brothers?
II Chronicles 14:1 is clear that Asa is the son of Abijah. What makes Hebrew genealogies difficult is that "son" and "daughter" are used to mean "male descendant" and "female descendant." It is a mistake to assume it is an immediate descendant every time. For example, "He [Abijah] walked in all the sins of his father [Rehoboam] which he had committed before him; and his heart was not wholly devoted to the LORD his God, like the heart of his father [grandfather] David" (I Kings 15:3). Since there are two "fathers" in this statement, one is qualified to make it clear which male ancestor is being discussed.
Another difficulty is that in different eras the same name is sometimes spelled slightly differently. Thus, it is believed that Abishalom is another form of the name Absalom, the son of David. Thus, it is believed that Absalom's daughter, Tamar (II Samuel 14:27) married Uriel, who was from Gibeah, (II Chronicles 13:2). They had a daughter named Maacah (or Micaiah as an alternative spelling), who married her cousin Rehoboam. Abijah is their son, whose name can also be spelled Abijam. Asa is their grandson.