Hi. Welcome to the forum.
To reverse pavement direction, You need to reverse spline direction in 3ds Max:
To set Drop Curb location, please set Material ID = 2 on the spline:
It looks like the width of the pavement is larger than the radius of the corner then unfortunately you will get this issue.
If the width is smaller but you are still getting overlapping polygons then increasing the Curve Steps value found in the style rollout may help to smooth the corner.
Maybe You can setup the scene so pavement goes outward, not inward to solve this.
To create Red Area With Flagstone You will need to extract area spline and use flagstone style with extracted clipping spline
Hope this helps or gives You direction how to move forward with this scene.