Yep, I included the delewares in the 'all those breeds' category, sorry I wasn't clear. But yep, those 3 breeds will mix nicely for you and lay very well.
Pullets are female chickens under 1 year old. Yes, white rocks are plymouth rocks. The breed is plymouth rock, color white. There are also barred plym. rocks, etc.
All those birds are good layers of nice brown eggs and you should be able to mix them without any problem once your younger girls...