Your focus is slightly misdirected. I'm guessing you didn't consider "brothers in arms" because the article is about an actual brother. However, the word is actually part of an idiom.
Here's an entry for arms:
1 Usually arms. weapons, especially firearms.
Now, in arms:
or under arms
armed and prepared for war
Now, that's the literal meaning. In everyday, figurative language, it means ready to fight.
Yes, they are actually brothers. However, the entire phrase here is brothers in arms:
in arms idiom
Definition of in arms
—often used in the brother/sister/comrade in arms to indicate one has helped to fight an enemy especially in a war
// He and I were brothers in arms.
Again, it is not literal in the sense that they go to war. It is figurative and used to say the players are a close, tight-knit group, like a group of men in the military who battle together. They happen to be brothers, and it has a double meaning in that sense, but the idiom can be used with any group, even if the members aren’t actual brothers.
As for a double meaning in in arms, yes, you could argue that there is one since the goalkeepers use their arms to play the game and capture the ball. You could also argue that there is also a double meaning in the usage of fraternity. It's being used to continue the metaphor of a close group of men being brothers, but fraternity literally means brotherhood:
A fraternity (from Latin frater: "brother"; whence, "brotherhood") or fraternal organization is an organization, society, club or fraternal order traditionally of men associated together for various religious or secular aims. Fraternity in the Western concept developed in the Christian context, notably with the religious orders in the Catholic Church during the Middle Ages. The concept was eventually further extended with medieval confraternities and guilds. In the early modern era, these were followed by fraternal orders such as freemasons and odd fellows, along with gentlemen's clubs, student fraternities, and fraternal service organizations. Members are occasionally referred to as a brother or – usually in religious context – Frater or Friar.
I don't think the writer is referring to an actual club of goalkeepers. It's just being used to convey the close relationship.