The "2 brothers" story is a myth that is perteputated in almost all family and is rarely true. The spelling of a last name is the least and last concern in family research. Surname spellings were often the result of someone who could spell, writing it as it sounded. If the illiterate peron couldn't read or write, how could they spell?
Tabor/Tabor/Taybor/Tayber/Taybour/Tabour, etc - its all the same.
This whole Sir John myth has been taken on by every early English Tabor line in America, including the Southeren lineage. I have spent 20 years researching the heritage of William Tabor/Tabor found in Henrico CO VA and died here in 1713 and found no parents or place of origin.