Does the leather being hard interfere with inserting and drawing the gun in the holster? If so, you may want to wet-fit the holster to the gun. Run tepid water over the entire surface, inside and out for about 30 seconds or until the leather is pliable. Place the gun in a plastic baggie, wrapping it around the gun snuggly. Insert the gun in the holster forming the leather around the gun (ejector thumb piece, etc.). If necessary, use a wooden dowel with the end rounded to form the inside of the body. Allow to dry for at least six hours, then remove the gun and allow the holster to dry thoroughly. Put the gun back in the holster and work it around a bit until it draws smoothly...to suit your taste.
Depending on how you dye and wet-fit your holsters they probably will wind up hard. A light application of Lexol(R) Leather Conditioner will soften the leather by restoring oils. DO NOT OVERDO IT, HOWEVER! I use a spray bottle (that can be the container the conditioner comes in), spraying a light application on the outside of the holster, then wiping it off with a soft cloth (old T-shirt works great). if the leather is still very hard, repeat, but, again, don't overdo it. Do NOT use Neatsfoot Oil on the leather.
Stay well, Pard!