seventh day adventist

I've became friends with a Seventh Day Adventist who really takes his denomination's theology seriously. He tried to convince me that the Constantine changed the worship day to Sunday. I would like for anyone to recommend books on the following two topics, so I may choose one and give as a...

Grace and Peace, I refuted a chapter on predestination from a Brazilian Seventh Day Adventist and defended the doctrines of predestination according to Reformed Theology. However, this month marks one year that I came to believe in the doctrines of grace and I don't know everything...

I don't know too much about Seventh Day Adventists. Are there any serious problems in their theology? I have heard different things. Some say cult. Some say almost. Some say they are Christian but have misguided theology. Do we as reformed people have any common ground with them?