UPDATE:
I was able to get it mostly working.
The seeds register properly, and I still need to clean up the class files for the Blueberry, Maloberry, and Raspberry seeds to match the BlackberrySeeds formatting. Same goes for the block classes. As it stands, the example textures for the seeds work also. The seeds will plant, the crops will grow the appropriate amount of stages, and the crops will drop seeds and fruit. However, the textures for the crops still do not load. Additionally, the item names are not correctly displaying, the creative tab name is not correctly displaying, and the items do not show up in the creative tab. I do still have a fair bit of work to do but I feel as though I've got a much better handle on modding 1.12.2 as far as this is concerned. My next project is going to be in 1.14, so that will be interesting. Thanks all for the help!