The Three Angels Messages, page-130

But I don't understand what you mean by "You have to attribute verse 8 to Christianity."

whereu would have to attribute verse 8 to Christianity for it to apply to the corruption of Christianity.

Do you consider them to be the Christians as well?

No. Not all all. Never.

In the verses quoted above, who are those people with whom God will dwell?

Well, cuz, it won't be you. Not at that time. Unless you repent and become a brother or sister in Christ in the meantime.
So, yeh, they are brothers and sisters in Christ, children of God. Presumably Christians. The Christians not involved in the great corruptuon we have yet to verify from verses in Revelations.

And which or whose God is being mentioned in the verses?

That would be the children of God. Brothers and sisters in Christ. Presumably Christians. The Christians not involved in the great corruptuon we have yet to verify from verses in Revelations.