That's just another misreading of adelphos, adelphe and/or adelphoi
These terms appear throughout scripture and are usually used in the sense of kinsman or relative.
Lot, for example, is called Abraham’s 'brother' (Genesis 14:14), even though he's the son of Haran, Abraham’s brother. He was actually Abraham’s nephew.
The term "brother" (Greek: adelphos) has a wide meaning in the Bible. It's not restricted to the literal meaning of a full brother or half-brother. The same goes for "sister" (adelphe) and the plural form "brothers" (adelphoi).
The Old Testament shows that "brother" had a wide semantic range of meaning and could refer to
* any male relative from whom you are not descended
* kinsmen such as cousins
* those who are members of the family by marriage or by law rather than by blood
* friends or mere political allies - for instance:
2 Samuel. 1:26
How I weep for you, my brother Jonathan! Oh, how much I loved you!
and in Amos 1:9
The people of Tyre have sinned again and again, and I will not let them go unpunished! They broke their treaty of brotherhood with Israel, selling whole villages as slaves to Edom.
And of His sisters, what fantasy dismissal do you peddle for them?