Let's talk about the Greek then. Where in the NT does Adelphos mean anything other than brother?
Matthew 13:55 Is not this the carpenter's son? is not his mother called Mary? and his brethren, James, and Joses, and Simon, and Judas?
Anything in that language lead you to believe that Jesus mother is not called Mary? Anything to lead you to believe that Joseph was not a carpenter?
Does anything lead you to believe that Jesus brothers from the womb are not James, Joses, Simon and Judas by the language in that text?
For one the word Brethren does (which implies close friends or cousins). But that's besides the point, There are many examples of it meaning anything other than a literal brother like in the Book of Acts when Peter was addressing the crowd at Pentecost.
Acts Chapter 2
[29]
Brothers, I may say to you with confidence about the patriarch David that he both died and was buried, and his tomb is with us to this day.
And again in verse 37:
Acts Chapter 2
[37] Now when they heard this they were cut to the heart, and said to Peter and the rest of the apostles, Brothers, what shall we do?
Theres about 20 more occurrences of that kind of usage in Acts and even more in the Pauline Epistles. Also in the Greek OT:
Genesis Chapter 14
[14] Which when Abram had heard, to wit, that his brother Lot was taken, he numbered of the servants born in his house, three hundred and eighteen well appointed: and pursued them to Dan.
Lot wasn't the brother of Abram, he was Abram's cousin, but the Greek still uses Adelphos.
I Chronicles Chapter 23
[21] The sons of Merari: Moholi, and Musi. The sons of Moholi: Eleazar and Cis.
[22] And Eleazar died, and had no sons but daughters: and the sons of Cis their brethren took them.
Once again the word Adelphos appears, and as you can plainly see the daughters married their cousins not their brothers.
Here are some instances where Adelphos refers to simply people of the same land or people.
Deuteronomy Chapter 23
[7] Thou shalt not abhor the Edomite, because he is thy brother: nor the Egyptian, because thou wast a stranger in his land.
Nehemiah Chapter 5
[7] And my heart thought with myself: and I rebuked the nobles and magistrates, and said to them: Do you every one ex- act usury of your brethren ? And I gathered together a great assembly against them,
Jeremiah Chapter 34
[9] That every man should let his manservant, and every man his maidservant, being a Hebrew man or a Hebrew woman, go free: and that they should not lord it over them, to wit, over the Jews their brethren.
II Kings Chapter 10
[13] He met with the brethren of Ochozias king of Juda, and he said to them: Who are you? And they answered: We are the brethren of Ochozias, and are come down to salute the sons of the king, and the sons of the queen.
[14] And he said: Take them alive. And they took them alive, and killed them at the pit by the cabin, two and forty men, and he left not any of them.