But Greek does have words for brother, cousin, uncle and aunt. God chose to inspire the use of the Greek word for brothers. Take it up with Him.
You are right, and of course these were the Lord's brothers and sisters. However, they were not the Blessed Virgin's children. The reality that many miss is that, from the earliest history of the Church, it has been held that St. Joseph was an aged widower who married the Blessed Virgin, at the call of God, in order to protect her. He already had children of his own, and these are the brothers and sisters of the Lord because they are are the children of his earthly father. They may also be his cousins, as some maintain, but that is not why they are called his brothers and sisters.
“You are right, and of course these were the Lord’s brothers and sisters. However, they were not the Blessed Virgin’s children. The reality that many miss is that, from the earliest history of the Church, it has been held that St. Joseph was an aged widower who married the Blessed Virgin, at the call of God, in order to protect her. He already had children of his own, and these are the brothers and sisters of the Lord because they are are the children of his earthly father. They may also be his cousins, as some maintain, but that is not why they are called his brothers and sisters”
An interesting story, but unsupported in Scripture and contradicted by Scripture.