class Program
    {
        static void Main(string[] args)
        {
            // Количество общих элементов
            var commonItemsCount = 2;

            var data = new[]
            {
                new[] {1, 2, 3},
                new[] {2, 3, 4, 5},
                new[] {1, 3, 5},
                new[] {1, 2, 3, 6, 7}
            };

            var q =
                from a1 in data
                from a2 in data
                where a1 != a2
                let c = a1.Intersect(a2).ToArray()
                where c.Length >= commonItemsCount
                select new { a1, a2, c };

            var selectedItems = new HashSet<int[]>();

            // Результат
            var result =
                (from g in q.GroupBy(v => v.c, new ArrayComparer())
                 orderby g.Key.Length descending
                 select new
                 {
                     // Общие элементы
                     CommonItems = g.Key,

                     // Массивы, содержащие эти элементы
                     Arrays = g
                        .Select(v => v.a1)
                        .Concat(g.Select(v => v.a2))
                        .Distinct()
                        .Where(v =>
                        {
                            if (selectedItems.Contains(v))
                                return false;

                            selectedItems.Add(v);
                            return true;
                        })
                        .ToArray()
                 })
                 .Where(v => v.Arrays.Length > 0)
                 .ToArray();
        }

        class ArrayComparer : IEqualityComparer<int[]>
        {
            public bool Equals(int[] x, int[] y)
            {
                return x.SequenceEqual(y);
            }

            public int GetHashCode(int[] obj)
            {
                return obj.Aggregate(0, (a, v) => a ^ v.GetHashCode());
            }
        }
    }