If you cheated with an identical twin, no… they can’t tell, with a run of the mill paternity test. If they are paternal twins, they will be able to check and see a difference. The only way they could tell with identical twins is if there are evolved differences. Our DNA can change due to environmental or triggered health conditions. If they could check that close, then they could tell if there was a difference, IF one of the twins developed a DNA change due to illness or environmental factors, then you would be able to tell, but I don’t know how definitive that would be. Markers for inherited DNA are basic. I don’t think we’ve come that far to be able to test the difference for identical twins.