I can comment very generally on 2. 2 does indeed look like a pair of leaves cut from a 16th century manuscript or at any rate the style of of the leaves fits with other early 16th century manuscripts. They depict the evangelists Mark and Luke with their respective symbols(winged ox and bull). My guess is that they were cut from their original manuscript by the dealers who framed them; it used to be a fairly popular practice to do this although you lose a lot of contextual information this way. If you want to research these leaves further my suggestion would be to take them to a local museum, university, or auction house and see if they can help you track down the manuscript they were cut out of; it may be possible to do this if the dealer's catalogs include other leaves from the same manuscript.

The inscription on the back of 4 says I think "Angelico painting, copied by Rocchio" and then a street address in Florence; given that this is quite clearly in the style of the painter Fra Angelico my guess is that it is a modern copy of a Fra Angelico painting?

The book leaves look legit. The art gallery was a real place and their plate helps to establish provenance. It will need more verification than that, but I've dealt with a lot of illuminated Bible leaves of this era, and I see no obvious red flags.

The cross looks like Cloisonne

You may want to cross post this to /r/whatisthisthing in case you don't get the answers you're looking for over here.