Please consult a registered homeopathic practitioner as I am not a registered homeopathic doctor. Based on what you have mentioned, my reply would be as follows.
You have stones in the calyx 12mm (right kidney) and 18mm (left kidney), these don't obstruct the flow of urine and hence often painless and asymptomatic. All the preparations you are taking help is increasing urine flow, reducing pain, slow disintegration of stones. The preparations are usually effective is stones of a smaller size up to 6 mm or 8 mm and are given for a period of around 3 months. The stones you have mentioned are 1.2 cm and 1.8 cm, hence you may take a longer time.
Please follow the simple diet advise of plenty of water, you can also consider Lemon juice (that has citrate in it and this can reduce the size of calcium stones). Horse gram has a diuretic and anti-lithic (anti stone forming) properties and is good to be included in the diet. Avoid tomatoes, brinjal, spinach etc. You haven't mentioned now long you are taking these preparations for. Are you a diabetic. If it's around 3 months, then I would suggest to recheck with a scan. If you are a diabetic then please be cautious about increased chances of developing an infection in the kidneys.