Sorry for bringing you bad news but you have read the problems of the hatchling failure syndrom.
I think Rhaes kidneys are damaged from a to dry start by the breeder. Kidneys that don`t work properly can`t get all the waste out of the body. The body can get rid of the acid in the blood of the sick tortoise. The body tries to compensate this with calcium that is taken out of bones and shell.
That`s why the plastron is getting softer. I am sorry but it seems to me that your baby is very sick and maybe will die.
I would try to put your baby for 6 hours every day in a plastik tub with warm shallow water and place it near a uvb producing heat lamp. Be sure that the water stays warm but the tortoise is not getting to hot. You can feed your baby in the water. That is no problem.
Only water can now help the damaged kidneys. There is only a little hope but I would try this. The hours in the water won`t hurt your baby when the water is warm, believe me.
Thank you I will try his out. I’m also taking Rhae to the vet Friday but I don’t know what they can do to help if anything at all. Could calcium injections be beneficial?