Those are a wide variety of rocks that have most likely been in a river somewhere to get the round shape. That often means they will have lost most of the soft parts so that they will not change the PH, GH and KH of most water. But we never know what may have happened to them since leaving the river so I always like to sterilize anything that goes in the tank. While there may not be anything on them, I feel better if I know my plate has just been washed and I feel the same about my tank stuff. So I would fill a container with enough water to cover the rocks and then add something like a tablespoon of cheap bleach that has no color or scent added. The chlorine in bleach is a chemical that reacts very easily with most any organic and that will clear almost anything just as it does in our tap water. The only difference in a bleach soak and tap water is the amount of water diluting the chlorine so once done soaking, I rinse it off and let any remaining chlorine gas off as it dries.
At that point, you have good hard rocks that you know are clean so good to use.
Those who fear bleach the most are those who did not get to watch their mother wash their diapers in bleach water!