public static bool AreSiblings <TVertex, TEdge>(this IBidirectionalGraph <TVertex, TEdge> graph,
TVertex vertex1, TVertex vertex2, EdgeDirection edgeDirection)
where TEdge : IEdge <TVertex>
{
var vertex1Parents = graph.GetNeighbours(vertex1, edgeDirection);
var vertex2Parents = graph.GetNeighbours(vertex2, edgeDirection);
return(vertex1Parents.Intersect(vertex2Parents).Any());
}