Use monobehavior functions in own classes

Hi guys, its me again.

And again I got a problem with custom classes and the wait function.

I got some new classes like this:

 //My Parent Class, its mainly for all the other classes to  //inherit from
 
 public class A{
 //some stuff
 } 
 
 //some classes with actual functions
 
 public class B : A{
 //some stuff
 }
 
 public class C : A{
 //more stuff
 }

I create some of my B and C classes in a simple function from a class that inherit the MonoBehaviour.

it looks like

 B test = new B();
 B.CallAFunction();
 B.CallAnotherFunction();
 ...

Well, now to my big problem: I want to usw the yield WaitForSeconds(x) in my classes B and C. A simple solution would be that A inheritates from MonoBehaviour. The problem with that, is that you can't use the new operator to create a new instance of an object of B's and C's then since MonoBehaviour won't allow that.

The question is, how can I create multiple objects from Typ A, B and C with using the yield WaitForSeconds(x) in it?

Thanks for any help.