Well I've heard both but there is no "cousin" in the link you gave. Trying to get "cousin" out of adelphos is stretching beyond reason.
Well I’ve heard both but there is no “cousin” in the link you gave.
And I strongly agree with you that it is a stretch beyond reason.
When I first heard of this belief, here on FR, I realized that the reason they were making such a stretch was because some other belief they had depended on those not being His brothers. I’ve since seen a lot of that sort of thing from others as well as myself: Interpreting a scripture in a goofy way because if it means what the plain language means, some other belief I have has just been skewered or called into question.