class Family
{
    private string last_name;
    public virtual string LastName { get { return last_name; } set { last_name = value; } }
}

class Father : Family{}
class Mother : Family{}
class Child : Family{}

Family f = new Family();
f.LastName = "Smith";
Father fa = new Father();
// When I do this, I get back a blank value
Console.Write(fa.LastName);

fa.LastName = f.LastName;

class Family
{
private string last_name = "Smith";
}

class Program
    {
        static void Main(string[] args)
        {
            Family f = new Family();
            f.LastName = "Smith";
            Father fa = new Father();
            //provide the class with the family you want to use
            Father fa2 = new Father(f);
            Mother mom = new Mother(f);
            
            // When I do this, I get back a blank value
            Console.WriteLine(string.Format("father's last name = {0}", fa.LastName));
            // When I do this, I get back the last name
            Console.WriteLine(string.Format("new father's last name = {0}", fa2.LastName));
            Console.WriteLine(string.Format("mother's last name = {0}", mom.LastName));
            Console.ReadLine();

        }
    }

    class Family
    {
        private string last_name;
        public string LastName { get { return last_name; } set { last_name = value; } }
    }

    class Father : Family
    {
        //base ctor
        public Father() { }

        //overloaded ctor
        public Father(Family incomingFamily)
        {
            base.LastName = incomingFamily.LastName;
        }
    }
    class Mother : Family
    {
        public Mother() { }

        public Mother(Family incomingFamily)
        {
            base.LastName = incomingFamily.LastName;
        }
    }
    class Child : Family { }