I looked at the Census Collection in Ancestry.com and there are over 152,000 men with the name, Clarence Davison. :o)
In order to narrow this down, you would need to supply middle name; approxmate date of birth.
Other useful info would be spouse's name & dob, as well as children.
I know by experience that there are no names that I've ever looked for that were not common to hundreds of people.
Think of looking for William Johnson in New York City. You could wonder the streets the rest of your life. But with further info, you could narrow it down. :o)
Any other info on the Sister, such as married name, where born, where lived, where her son was born; approximate years of birth for either...
Then we would have a better start.