You need something like this: Pactech: 5v DC fan wire splitter 4" 4P2C ( 2 ) to 2 x 3P2C ( M ) Wide side is Molex 4 pin split into 2 3-pin connectors, there are also many more similar connectors.
It is so simple, yet it is so difficult to find on internet. This is Pactech product list in pdf, I wish it could be more clear, so you can see all options.