The man was arrested at an address in south London on suspicion of both murders and remains in custody.
The sisters were stabbed to death at Fryent Park, off Slough Lane. They had been there earlier to celebrate Bibaa’s 46th birthday.
Detective chief inspector Simon Harding, leading the investigation, said: “Given the significance of this development, we visited the family in person today to inform them of the arrest. Our thoughts remain with them at this very difficult time.
“A team of forensic officers have been a constant presence at the park over the last few weeks carrying out meticulous fingertip searches at what is a vast and complex crime scene.
“Whilst that work has now concluded, smaller searches in outer areas of the park will continue.