Although the band members of Christian Death are Christians, the band is not a Christian band. They are a secular rock band.
No. They're a secular band with a "few good songs"
No, Hellogoodbye is not a Christian band. However, some of their lyrics may have a Christian meaning, but that does not make them a Christian band.
Yes, it is
Yes, it is. Their religion is highly evident on many of their songs, especially I Stand.