alls I can say is that the Wyandotte's tend to lay a lighter chalkier egg than all my other brown egg layers but that's just the wyandottes I have/had and I doubt every line of Wyandotte has the same characteristics as mine. you really need to have a separate coop/run/nesting box and do one chicken at a time to figure who who laid what. And eggs characteristics change over time for the same bird (or can change) so what they are laying in fall is not what they may be laying in spring.
The egg with speckles (2nd from left), looks exactly like the egg one of our Black Australorp lays consistently. The other 2 BAs that we have do not lay a speckled egg. The other brown egg layers we have (SLW, BJG, BR) also do not lay a speckled egg. This leads me to think the speckling might be an individual trait rather than a breed trait.
I’ve heard that some people have used food dye on the vent of a laying hen to tell who is laying what. Your chickens backside will look a bit odd for a day or so (red?, blue?, green?), but if the egg ends up with streaks of that color, you should know who laid what. Otherwise, the less messy way is what @Compost King nentioned: separation till they lay.