Complex sentence: They were given preference to handle the domestic trade of the islands and to lease land from the friar estates through the "inquilino" or lessee system, that allowed them to sublet those lands.
Split into simpler sentences: They were given preference to handle the domestic trade of the islands. In addition, they were allowed to lease land from the friar estates through the "inquilino" or lessee system, that allowed them to sublet those lands.