You will need an enemy class simlar to your player class remember that since you are making more than 1 instance it cannot be static.
You will need a list of this class to hold your enemies.
List<Enemy> Enemies = new List<Enemy>();
Now you can add enemies with a random position (make some paramaters for the position in the enemy constuctor)
Random r = new Random();
...
Enemies.Add(new Enemy(new Vector2(r.Next(0,100),r.Next(0,100));
And when you need to update your enemies you can add a method in the enemy class and have this call it
foreach (Enemy enemy in Enemies)
enemy.Update(...);