I need to process Sentinel-2 L1C images of an area on different dates. I want the Time series images to be radiometrically normalized. Are they already normalized? If not, then can anyone please share how I can do this in python.
No, they are not. What you are looking for is L2A data, see ESA’s user guide for more information:
https://earth.esa.int/web/sentinel/user-guides/sentinel-2-msi/product-types/level-2a
You can use L2A within Sentinel Hub:
https://www.sentinel-hub.com/faq/what-kind-atmospheric-correction-available