People often call anything that is white and not a Leghorn a RIW. That poor breed name gets abused and misused. The RIW has a rose comb and is an incredibly rare breed. 99% of the time, these mis-labeled birds have single combs and no evidence of rose comb in the genetics.
They're just mixes. They are chickens and probably be just fine. Since people always have this felt need to have some breed identifier, this kind of thing happens. 95% of the world's chickens aren't any breed.
If they are healthy and do well for you, that's great. Enjoy them.