Sadly the real Willie became blind due to firecracker incident.
Sherri Stoner (Rachel) is 8 years older than Jonathan Gilbert (Willie) although they were supposed to be about the same age. Sherri is 5 years older than Melissa Gilbert. Age close enough to date Dean Butler since she wasn't a minor like Melissa Gilbert since she was 17 and Sherri was 24..
Interestingly enough, the real Caroline Ingalls and Mary took boarders into the home Charles built in DeSmet South Dakota. They needed extra money after Charles passed away in 1902.