The first three feet are a set of top stitch feet of different widths, one set looks like a double welt foot, but it's hard to tell. The other two black ones are single right feet which you can use to sew the plastic pieces back on the seat cover. I'm not sure what the silver one is, it could be a presser foot, but I'm not sure.
The fabric looks like the scrim backing on sew foam. As far as the leather goes, that sounds like bull spit (substitute an "H" for the "P") to me....I've never seen an upholstery hide like that. Voids in the hide generally mean it's a lower quality hide.
No one lives forever, the trick is creating something that will.