you look to have two very nice crays there. i agree though there are what look like signs of shell rot, the offered solution is imho the best.
my main concern though is the use of RO, you dont say how you treat this water. but i feel you must know that Crayfish absorb the calcium they need to make their shells, from the water around them. not as you might expect, from the food they eat. if you are not making up the shortfall, caused by your RO system, this could be the reason, or one of them, for the shell rot.
About six weeks ago the two Crayfish in the store where i work bred, at first we fed them on liquifry before they moved onto bloodworms and brineshrimp, they seem to be doing well and are now about half an inch in size, they are all still in the same tank as the parents are seem to be doing fine