Hi James!
Welcome to the group!
Based on the images, the gemstones might be something other than diamond. It is really hard to identify just from images alone. There are a few tests you can do to help determine what they could be. The first test would be specific gravity.
Here is a YouTube video on how to measure specific gravity.
Here is an IGS video link to a similar test setup. (I am not sure if this link is working correctly, though)
The formula for calculating the specific gravity of a gem is:
Diamond has an SG of 3.51 to 3.53. There are a few other stone species, that can have a similar SG, so this doesn’t completely rule out diamond if you measure somewhere in that range.
The Gemstone Encyclopedia here at IGS has an really neat advanced filter where you can narrow down the specific gravity range of potential stone species.
Let us know what you measure for SG and we can then start selecting other tests to perform.
Cheers!