[blue-duncan]

" unless the parents are identified, we'll never know by the deisgnation "adelphos" alone if broad kinship,"

So we don't know whether Andrew and Peter were brothers or whether Lazarus was the brother of Mary and Martha?

[annalex]

we don't know whether Andrew and Peter were brothers [in the modern sense of children of the same parents] or whether Lazarus was the brother of Mary and Martha?

No, strictly speaking we don't know that from scripture alone, unless there is a passage somewhere in the scripture(?) that lists their parents.