Q: Is it possible to get Silicone stains off from denim and cotton?

A: It would be helpful to know the source of the silicone. I worked on ArmorAll and we used a lot of silicone for our protectant and tire products. The important thing here is to use a good product with lots of surfactants like liquid detergent to pretreat prior to washing (apply; rub into stain; wait 5-10 minutes) in HOT water using liquid detergent.

The good news is these are cotton fabrics here rather than a poly/cotton blend, which would hold the silicone much more tightly than cotton.

Don't forget to check for success before drying as it will make any un-removed silicone much more difficult/impossible to remove. If there is still silicone remaining you can retreat fabrics again.