Here is some more photosWelcome from Maryland! Unfortunately I am in agreement with @ucvrelics, for a few reasons:
1. The star buckle should be stamped brass, but appears to be cast, beyond that it is doubtful such a dainty plate would have lasted until Gettysburg. Plates such as this are found in early war sites, due to their fragile nature.
2. NY buckle, @ucvrelics has a good point about the bench marks, but due to the private purchase of officer's buckles, they came from many sources and not all have the stamped or cut bench marks. Because #1 is most likely fake it taints the others unless we can get provenance and who these were purchased from. The buckle strongly appears to be a Gary Williams product, with exception of the bend of the hook.
3. CSA piece, the sloppiness of the casting is a little too much even for a CSA piece and the hooks look too good, but would need to see measurements and provenance.
Where did you pick these up and approximately what did you pay for them will give us a very good idea, were these all in the same collection? I remember in my early days of collecting I was told by a respected member of the collecting/dealer community, "when in doubt about a buckle, don't pay more than a happy meal"