Offset curve direction not solved after unify curve direction

offset multiple curve after use twincurve, but it end up with the different direction ,even after I have unify the curve direction use flip curve.
please help. Q_Offset curve (9.1 KB)

If you make a surface using your base curves, then you’ll know they won’t create a planar surface.
So, that means, your tween curves will not on the same plane and It’s hard to determine which plane is the right one for your offset base plane.
BTW, Here we have another alternative way of doing it by using Offset Surface.

Q_Offset curve (13.0 KB)

Thanks Kim, your solution really helps, But just to understand here , any thought on why flip the curve directly to the same does not help with the offset

Remove the XZ plane