I’m not Mormon, but your questions made me curious. I did a few minutes of research and found the Orson Hyde, who was one of the Quorum of the 12 apostles taught your question #1 in the Journal of Discourses, volume 2 to which I will provide a link later in the post.
Orson became a disciple early on in the ministry and was deemed an apostle by Joseph Smith Jr. Approximately 20 years later he spoke against the saints and left the church. He repented later and asked to be brought back into the church (which he was). Instead of succeeding Brigham Young, Taylor was chosen instead. Young was critical of Hyde’s leaving the church.
According to different sources the Journal of Discourses were standard doctrine, but not infallible teaching. I suppose it’s similar to the Pope speaking “ex-cathedra” as opposed to simply giving a speech about his own views. I could be wrong, but that’s the similarity that comes to mind.
Here is the link: