One was born in 1718 and the other in 1720. It could be that the first one died very young and when the next son was born, he was given the same first name as the one who died young.
My 3rd great grandfather had a brother who died young and the next son was given the same first name as the one who did not survive beyond early childhood. Laurence Gill was born in November 1759 and died in 1759. Two years later in November 1761 the next son born was also named Laurence. Both were born in Norfolk County, England.