I'm guessing the majority of extra eggs are coming from the black sex links. I have two BSL's and one of them would give me two eggs every 24 hours several times a week when she began laying. This went on for several months. At about 1 1/2 yrs., she began having problems with that 2nd egg. She'd take on an odd posture, would quit pecking, scratching and would generally act ill. Several hours later I'd find an egg in the run instead of the nest. I thought for sure she was getting ready to be egg bound but she always managed to eventually lay that second egg that seemed to be causing her problems.
 
At this point she's almost 3 years old and hasn't laid an egg since last summer. She's become fat, didn't molt like the rest of the chickens, but is absolutely beautiful with lovely shiny feathers as she's not using her nutrition for anything else. She's mean as a snake, picks on the other chickens, and is destined to be the star in my son's birthday Chicken Pot Pie dinner. Her sister is still laying an egg daily but she never did the two egg a day thing.
 
I hope that your girls will not have any issues like my one girl did. I also have barred rocks and they're consistent layers but have never given me doubles. The sex links are bred for production and I think my one girl was an over-achiever early on but her bright candle has since burned out. For that reason, I'll not have sex links again. They have a reputation for heavy laying in the beginning but burning out early.