REYES might mean "KINGS", as in De Los Reyes.
However, it could also be a patronymic name.
Patronymic names are common in Spanish. Example MARTIN+ EZ = MARTINEZ (SON OF MARTIN). Perez, Sanchez, Rodriguez, Rodrigues, Vasquez, etc. It is much the same in English, for example Martinson, Johnson, Jackson, etc.
REY + ES = SON OF THE KING
Remember that Spain wasn't a unified country until 1492, when the last Moorish King of Granada was defeated by Ferdinand and Isabella. It was many centuries before their descendants had a unified kingdom. Therefore there were many KINGS in Spain, not just one. It is likely that someone might be Juan Reyes (Juan the son of the King).
