The photo of Jerome was in a case with the "D. H. Spencer Artist Hudson. M." impressed in the velvet opposite the photo. The photo of Amelia has the artist's identification impressed on the bronze mat around her photo.
The photo of the brothers together is a daguerreotype, while all of the others are ambrotypes. This helped in narrowing down the dates that the photos could be taken. Spencer started producing ambrotypes in 1859. While no date is listed when he ceased producing ambrotypes, with the advent of the "tintype" process, ambrotype production pretty much ceased by the end of the Civil War. Thus, in theory, the last date any of these photos could be taken was ca. 1865. Obviously all of the brothers were deceased by then, but this helped narrow down with pretty good accuracy which sisters were in the photos.