I asked my wife to look at the pictures. She's curator of the local historical museum. One of her specialties is vintage and antique clothing.
Judging by the "puffy" sleeves, the collar and the pattern of the dress, 1890 to 1910, plus or minus two years.
Younger women wore more up-to-date styles. She could have been between 16 and 20 years old at the time of the photograph.
Looking at the older woman's dress, the style dates approximately twenty years sooner.
Older women don't often "style shift" and are more likely to keep wearing the same kinds of clothes that they wore when they were younger.
The picture could have been taken at approximately the same time period as the younger but it is hard to tell.
For an example of this style difference, think of the TV show, "Downton Abbey."
Maggie Smith's character wears styles that date more to her younger years, compared to the more modern styles worn by the younger family members in the house. (e.g. Maggie Smith doesn't "style shift" and wears clothes that date from a previous generation.)
My wife did notice the embossed seals on the photos. She also suggests you run that down. A local historical society can assist.
The pictures, themselves, do appear to have been made in the late 1890's to early 1900's. No later than 1915, she says.
That's pretty much all she can say from looking at a digital copy on my iPad.
If you need more, you can look for a professional archivist. An archivist is probably going to want to see originals, though.
If you need an archivist, she can probably get you in touch with one but, it's not going to be a free lunch.