If you’re using the original iRig that plugs into the iPad headphone jack you’re getting crosstalk.
There is NO way to avoid this, it’s a limitation of using the headphone/mic jack.
Tons of USB audio interfaces are supported via the Apple(only use the authentic, not a knock-off) Camera Connection Kit.
Or get one of the newer iRigs like the HD or Pro that plug in via lightning connection, you’ll get pristine sound quality.
Carl