I stand by Kolokotronis' 681. You go by vernacular meaning and studiously avoid the original usage.
The listing of the name is the broad context that you miss. Mark gives a part of that list as children of Mary Cleopas.
The fact that "adelphos" was used to indicate spiritual kinship in absence of blood relation is alone a good reason not not replace it with the specific designation like xanadelphos or syggenos when applied to disciples who are also blood relatives.
And, where is your literalism when it comes to James 2?
"The fact that "adelphos" was used to indicate spiritual kinship in absence of blood relation is alone a good reason not not replace it with the specific designation like xanadelphos or syggenos when applied to disciples who are also blood relatives."
You did not look at the verses that specifically identify apostles, disciples and brothers by distinctive words.
However there is a better reason for identifying them as the brothers and sisters of Jesus and that is the consistancy with which Luke, a Greek from Troas, uses the word in two letters to the same person. As mentioned in his first letter to Theophilus (the Gospel of Luke) he uses the word "suggenes" for cousin (Luke 1:36.) In the same letter he uses the term adelphos for brother when referring to Peter and Andrew (Luke 6:14) and Judas and James (Luke6:16). In Luke 8:19 he refers to Jesus' brothers using the same term that he had used for the previous brothers but not for Elizabeth.
In his second letter to Theophilus (the book of Acts) Luke again uses the term adelphos to refer to Jesus' brothers (Acts 1:13-14) that he uses for James the brother of John (Acts 12:2). When he uses the term adelphos to refer to members of a community there isn't any question because of the context i.e. they are being addressed or used as an illustration, not for filial identification.