If Mary had been married to someone who already had children they would be "Step Brothers and Sisters". If Joseph and Mary had children themselves they would then be "Half Brothers and Sisters".
Here is something else to ponder. [John 7:1-5] After these things Jesus walked in Galilee: for he would not walk in Jewry, because the Jews sought to kill him. Now the Jew's feast of tabernacles was at hand. His brethren therefore said unto him, Depart hence, and go into Judaea, that thy disciples also may see the works that thou doest. For there is no man that doeth any thing in secret, and he himself seeketh to be known openly. If thou do these things, shew thyself to the world. For neither did his brethren believe in him.
Here Our Lord is being taunted by......"His Brethren". Much is made of these words as being just "Brothers in Spirit"....so to speak.....or camp followers. No! these are flesh and blood half brothers who are taunting him to go anyway (to the Festival) because they knew the Jews had it in for him......and they wanted him dead! They were obviously very jealous of his power (verse 3) and they did not believe him (verse 5). This is not a good example of devoted "Brethren!" How anyone can read these verses and come away believing that these "Brethren" were just followers of Our Lord.......is beyond me.
[Mark 6:3-4] Is not this the carpenter, the son of Mary, the brother of James, and Joses, and of Juda, and Simon? and are not his sisters here with us? And they were offended at him. But Jesus, said unto them, A prophet is not without honour, but in his own country, and among his own kin, and in his own house. Early in his ministry he admits to not having any respect from these same "Brethren". They were well aware of His growing preoccupation of a mission....His confrontation with Satan was probably made known to them....and these folks, being typical blood relatives were thinking he was probably crazy [Mark 3:20-21]!
[John 2:12] After this he went down to Capernaum, he, and his mother, and his brethren, and his disciples: and they continued there not many days. This verse proves there was a definite distinction between His disciples (followers) and His brothers. It's almost comical (definitely goofy) how the main stream church goes to these lengths in attempting to show a perpetual virginity which is neither scriptural.....nor logical!
To my knowledge, the terms Step Brothers and Sisters, did not exist in the period under concern, and was certainly not widely used. Between the frequent early deaths and remarriages, and the cultural attitude that the definition of a family depended on connection to the father only, 'brethren' not the children of Mary makes much sense. I might go further, in the case of Catholicism, the Church believes that the Aramaic for brethren, includes first cousins, and that is what the Church believes Christ's brethren are.
I think that the Orthodox accept the idea that they were Joseph's children, and Christ's step siblings. Since the perpetual virginity of Mary is accepted by most Christian churches, only some 'low' churches think that they could be Christ's half-siblings (children of Mary). Naturally, if one things these brethren were full siblings of Jesus, you don't believe that he was 'the only begotten Son of God', and are not any kind of Christian.
Not comical, but sad, in my opinion.
Why waste all the time and prayers to someone who is DEAD and in their grave - awaiting the Resurrection like ALL the REST of the saints?