In addition midfielder Dani Ceballos has extended his loan from Real Madrid until the end of the current 2019/20 season.
Luiz, who signed from Chelsea last summer, has agreed a new one-year deal. Pablo will complete his formal move from Flamengo on a long-term deal when the transfer window opens next month. Cedric will also join permanently on a long-term deal from Southampton.
Technical director Edu said: “I am really happy that we will have these players in our squad for the future. They have been part of the long-term technical plan Mikel and I have developed. They bring the right balance to our squad.
“David is a really important player for us. He has played most of our matches this season and has been important for the team. His passing, his communication with the team on and off the pitch. He helps everyone.
“With Pablo we're all disappointed he got injured at Manchester City. Since Mikel arrived here he was asking for a central defender who was left-footed. We were really pleased with Pablo - his behaviour, the way he is training, his mentality and his quality. Unfortunately, he has that injury but of course we are really happy to keep him for the future.
“Cedric is also going to be an important player. He has been unlucky with the injuries but he is close to being ready and gives us more strength in the right-back position. We're also pleased Dani will finish the season here. He is making a good contribution and we look forward to him having a strong finish to the season."