1) SJ is probably the Danish maker S.A.J. Jacobsen in the town of Slagelse (1937 - 1973)
2) Why do you think this is Norwegian? I think it looks more like danish mark, and in that case it's Knud Georg Jensen in Copenhagen (1908 - 1948)
3) Agree that it's probably Norwegian. In that case the maker is Berhardt Hertz.
4) You have interpreted the Swedish marks splendidly! I might add that the figurative mark is Sweden's patron saint S:t Erik, which is the town mark for Stockholm.
Best regards / Matulda