I would say as follows:
1) a married couple ]
2) a brother and a sister carrying the same name (with parents f.i. dead)
— I would find this a bit strange; you'd be more likely to say "Ewelina and Eustace Brown".
3) a brother and a married sister (still regarded as a family)
— No, I don't think so.
3) brothers or sisters (alternatively for the Kennedy bothers, the Bronte sisters),
— The Brown brothers, the Kennedy sisters, etc. would be fine; though perhaps a little old-fashioned.
4) multi-generation family with all members alive (grandparents, parents, children, grandchildren),
— If they all lived in the same house, possibly. Otherwise, I don't think so.
5) a clan (in genealogy),
— No, probably not.
5) configurations like a widow after one brother and the second brother?
— No, quite unlikely!