Copying elements from unrelated Workplanes together is not supported in families. Try copying elements separately.
Namespace: Autodesk.Revit.DB
Assembly: RevitAPI (in RevitAPI.dll) Version: 26.1.0.0 (26.1.0.34)
Syntax
C#
public static FailureDefinitionId CannotCopyMultipleSketchParents { get; }