Passport applications for married women in the United States in the early 1900s included information on the citizenship status for their husbands or fathers (depending upon the marital status of the applicant). If the wife of your ancestor's brother applied for a passport during this time period, she might have given information on where and when her husband was born. Wives of two uncles applied for passports in the 1920s and gave detailed information on their husbands.
US passports from 1792-1925 are at Ancestry.com and at from 1795 to 1905 at Footnote.com.
Remember that only the passport applications for about the last twenty years provide information on the husband and that Footnote's really don't go recent enough to show husband/father information in most cases.