How is Joab related to Amasa?

Question

I’m having a hard time distinguishing this from the text. It’s clear that Amasa’s parents are Jithra and Abigail. It gets confusing to me after that.

“And Absalom made Amasa captain of the army instead of Joab. This Amasa was the son of a man whose name was Jithra, an Israelite, who had gone in to Abigail the daughter of Nahash, sister of Zeruiah, Joab’s mother.” 2 Samuel 17:25 NKJV (https://www.blueletterbible.org/nkjv/2sa/17/1/)

• Is Nahash the father or mother of Abigail?
• Is Nahash the “sister of Zeruiah” or is this referring to Abigail?
• Who is Joab’s mother?
• I’ve seen other posts that these questions may be difficult to answer, I’m less seeking to harmonize and more trying to understand if it’s possible to determine from the language alone. Are Amasa and Joab 1st or 2nd cousins?

I can see how this could be either:

1. listing all the things Abigail is.
   Abigail is the daughter of Nahash. She is the sister of Zeruiah. She is Joab’s mother.
2. splitting from each statement to define the previous person. Abigail is the daughter of Nahash. Nahash is the sister of Zeruiah. Zeruiah is Joab’s mother

Answer 1

How is Joab related to Amasa?

The topic "Amasa" in the Insight on the Scriptures lists Amasa as Joab's cousin:

1. Son of David’s sister or half sister Abigail and Jether (Ithra), and cousin of Absalom and Joab. (2Sa 17:25; 1Ch 2:16, 17) Jether is called an Israelite in Samuel and an Ishmaelite in Chronicles, perhaps because he lived in Ishmaelite territory. Some contend that Amasa is to be identified with Amasai, one of those who joined David’s army at Ziklag, but such an identification is uncertain.​—1Ch 12:18. [bold mine]

This is also corroborated under the subheading "Murders Amasa" in the topic "Joab":

During the pursuit of Sheba, Joab committed a grave crime. As Amasa (who was his cousin; 2Sa 17:25; 1Ch 2:16, 17) came to meet him near Gibeon, Joab let his sword fall out of its sheath. [bold mine]

To better visualize the relationship, the printed and pdf version of the Insight of the Scriptures have the genealogy of David that shows Joab and Amasa's relationship

[Graphic of David's Genealogy from the Insight on the Scriptures pg 589]

[All scripture quotations from the New World Translation of the Holy Scriptures (Study Edition)]