Not if you read scripture which says He has brothers and sisters. The “assumption” is on the part of Catholics who try to somehow discount what the Holy Spirit had written.
Indeed. There is a lot on this thread based on Argument from Silence. There is no mention of siblings at the Nativity, nor in the Temple at 12 years old. There is a reason for that...
Such things are not relevant to anyone’s salvation or salvation history in general. It also takes attention off the Message by all those people (Dan Brown, et al) who are more concerned with the Bloodline, as if we worship specific genetic markers and not His divinity.
Divinity is not in the DNA, which is of the body. It is philosophical / theological. Assuming you could get hold of the the actual blood spilled at the Crucifixion or if it is on the Shroud of Turin, there is nothing there you could clone or splice into someone else to make them divine.
All these philological discussions about brothers versus cousins are nothing more than flights of fancy.