Select
de1.*
From [DataExtension1] de1
Left Join [DataExtensionSplit_1] split1 On (de1.[Email Address] = split1 .[Email Address])
Left Join [DataExtensionSplit_2] split2 On (de1.[Email Address] = split2.[Email Address])
Where split1.[Email Address] Is Null
And split1.[Email Address] Is Null
/* writes to DataExtensionSplit_3 */