Watford have signed West Ham United full-back Jeremy Ngakia on the same day as seven players left Vicarage Road.
The 19-year-old was out of contract at the Hammers, having made five Premier League starts, and joins the Championship side on an unspecified contract.
Hernandez has joined Getafe on a season-long loan, having spent the last two years out on loan, while the Spanish club have exercised the option to turn Foulquier's loan into a permanent deal.
Brazilian midfielder Santana is also heading to Spain to join Recreativo de Huelva on a permanent deal, while Sibo will stay at UD Ibiza for a second season on loan.
Elitim has joined Ponferradina, Alvarado has signed for Brazilian outfit Club Athletico Paranaense and Velasquez is staying at MLS side Portland Timbers.