You can do a few things differently, but my first advice is to contact a certified barefoot trimmer in your area to work with you on this. Shoes will not help your horse's hoof. they impair the circulation needed to strengthen the hoof. A proper barefoot trim will get the hoof tissues perfused with blood, which delivers the nutrients and moisture to the hoof structures.
Hoof wall grows down from the coronary band. but new research has shown that lateral pathways also develop within in hooves when they are trimmed correctly. These allow for thickening of the hoof wall from the sides (inside the hoof) as well as the growth downward from the coronary band.
Farrier's Formula contains the correct amino acids and is recommended over all of the other products which don't. Hoof structures are formed from specific proteins (amino acids) and are built from the ones contained in Farrier's Formula. This information does not come from the company making the product, but from veterinary research. Soybean meal also contains these amino acids. Biotin supplementing has not been shown to have any beneficial effects for hooves. Unless a horse is deficient in biotin, which is almost never the case, it is a waste of money.
The hoof wall needs to contact the ground and expand and compress in order to function as it is intended, and shoes prevent this.
Hoof dressings do no good and can be harmful....they harbor bacteria and fungi next to the hoof wall, which is made of keratinized protein. The germs digest the keratin, making the wall soft. this is not good. You want the keratin to be hard and sturdy, so don't put anything on it.
The crack has to grow out from the top down, but the wall can be thickened and stabilized all along the length of the crack if the tissue can be perfused with blood adequately. the hoof has to function correctly for that to happen. Then the amino acids provided in your horse's diet and needed to build hoof wall will be available to form tissue, and with the right trim, the lateral paths will form to develop new tissue that can thicken the walls.
The soles should be allowed to thicken and form callus, and naturally shed. Using Venice turpentine is a temporary fix that does no good in the long run.
So, my advice is to find a barefoot trimmer. they are specifically trained in the art of trimming a barefoot horse, so your regular farrier is unlikely to possess the same skills and training.
EDIT....oh well......if you get the chance to learn how, it sounds like your area could use a good certified barefoot trimmer ! Maybe you can talk your farrier into getting some more training ???