I did half look, but first reaction was “don’t know”. 
I’ll try and focus a bit more for you. Detective hat on.
Qu1: I would keep the full name for the Series as this is what it says: “Integrity Music’s Scripture Memory Songs”. Though I would NOT add that to the Release titles as they have their own shorter titles.
Qu2: Just “God’s Grace”. Then link it to the series. In this situation I especially focus on how they use the short two word title on the rear cover. The graphic artist is focusing on the real title.
It is part of a series, but that isn’t part of the title. (As can be seen clearly on the CDs in the following question)
Qu3: This is tricky. When looking at the edit history of Discogs it is clear that the cover was uploaded separately to the rest of the images. There is a slight change on that cover between the image at Discogs and the one on Ebay. Hard to know if the original editor at Discogs has uploaded a real front cover or sourced an image from elsewhere.
Do you own this? Is your copy like EBay? If I was adding it, then I would just add my copy. I distrust that cover at Discogs.
Aha! Search Ebay more and you will see Discogs has mixed TWO separate releases. The REAR covers are also different. Most releases on EBay use the Ebay cover you found above, and the rear images from Discogs.
But look at this one:
That is showing the Discogs front cover and a DIFFERENT rear cover. Notice the box around the title.
So there are two copies, same barcode. Discogs is misleading here as they have mixed the two releases.
Using EBay in the search is really useful here. I don’t do that enough. Interesting idea.
Qu4: Now I am not really sure. This is done as a group project, so Spotify have some logic to how they have titled it. The Soloists are just one person who has stepped forward in the group to sing. I guess this is choral music? So they are really known by a group name for the choir. This is where you add the soloists into the Relationships as a Lead Vocal.
Not really sure about No 4. I’d want to look more as to how the other releases are crediting the artists.