If I have this right, I think you will need two Y's. One Y harness would go to both right ail. servos and plug into the
Ail slot on the RX . then use the other y harness for the two left servo's and plug into one of the extra channels. Might have to be flaps, is you have that channel.

On my JR x9303 I will turn on flaperon in the wing section. I have to reverse one of the servos for one of the channels to get the aileron function. With out the servo reverse you have flaperons.

Thats one way to do it. there may be another . and thats on my radio not sure on yours.

sticks