I'm sorry for the loss of your mother.
To me they all look like imitation pearls except for photo #3.
The pearls in photo #3 are off round; some have the eggy / potato shape typical to freshwaters. Please check the clasp with a good magnifier or a jeweler's loupe for marks indicating what metal they are. These would not be valuable pearls, but they could be real cultured pearls.
Unfortunately pre-owned pearls do not tend to sell for much. And imitations, especially in grimy condition with broken thread, are hard to resell at all.