Do all axolotls grow to the same adult size, or do they vary?

Check water chemistry and temperature first. Axolotls are very sensitive to changes in either. If ammonia or nitrites are elevated, perform partial water changes using conditioned water that is temperature matched. They do best between 60 F and 64 F. Water temp above 75 F is stressful. Fast her for a few days to see if she passes a large amount of stool. If she does, resume feeding her as scheduled. If she doesn't improve, consider "fridging" her to reduce stress and allow for recovery. You can read about the fridging routine at the link below. https://www.caudata.org/forum/showthread.php?t=85263

Even though Orux is smaller than his siblings, he can still grow to close to full size. He may be a bit smaller than them when he becomes an adult, but he should be around their size. Keep in mind that every breed has a range of sizes and weights, and dogs within that breed can go anywhere on the range. So even if he's on the smaller size, he will still be within the normal range for a Rottweiler. Only time will tell how big he will become. I hope this helps.

Check the water quality and temperature. Perform partial water changes every few days to maintain pristine water quality. Use only conditioned water that is temperature matched to prevent further stress or shock. Clean water is the foundation for healing and recovery. If there is no change, consider an exam with your veterinarian or a vet experienced in treating axolotls. They can be sensitive to medications, so a doctor's advice after an exam would be safest.

I really think you need to go with the recommended temperatures. Temperatures that are too high (over 74F) are associated with heat stress and death in these guys. An ideal temperature range is the low to mid 60s. An aquarium chiller is recommended if you cannot get the temperature low enough. I suggest you refer to this article: ( http://www.reptilesmagazine.com/Care-Sheets/Frogs-Amphibians/Axolotl/ )

Treating him yourself would not be recommended as you may cause injury. If the rock was small, he may eventually pass it. Maintain pristine water quality and proper temp. Monitor his appetite and stool output. If there is a veterinarian nearby with experience treating axolotls, then an exam would be strongly recommended in case surgery is required to remove the rock. Fridging Nox may also be recommended. You can read more about the process at the link below. https://www.caudata.org/axolotl-sanctuary/Fridging.shtml

Depending on diet and environment, it may take as long as 5-8 years (or longer) for her to reach adult size. Female turtles typically take longer to grow since they are bigger than males. Blanding females also mature sexually much later (14-20 years). Because of this, they are considered "endangered" throughout most of their range.

If you don't know the birth date, size is the best (but not most accurate) method to determine age. Adult emeralds are about 6-8 inches long when fully grown. This length can be reached anywhere between 6 and 12 months. It depends greatly on environment and diet/nutrition and can vary bewtween lizards.