[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.

[blue-duncan]

And you don't know from scripture whether Jesus had brothers and sisters since from your point of view, if the names are not linked to a parent, they could be siblings, relatives, friends or members of the common community.