1 big issue and complication : rekordbox interface 2 using control vinyl - high pitch sound

Hi, I have 1 big issue first to explain and after a complication. The big issue is I use control vinyl on Pt1 scratch with control vinyl serato / rekordbox vinyl also Rekordbox interface 2 Behringer DDM 4000 Using Rekordbox software. There is this super high pitch sound and when I record it , it's also there. The stylus is the original, I'll bought the diamond stylus these days. Maybe the sound will gets better but the high pitch sound will stays ? How to avoid this sound ? Also the complication. Situation, my dj setup Is 2 cdjs 850 Pioneer so I've plugged them with usb cables to my MacBook, the outputs on the interface 2 in a channel inputs on the mixer. The pt1 out to input 2 on the interface 2, the output 2 of inferface 2 to an input on the mixer. The problem is my setup is 3 turntables : 2 cdjs ans 1 turntable using dvs. Can I put 2 splitters RCA (mono male to 2 RCA female) on a output lof the interface 2 then connect the 2 different input channels on the mixer ?