You can use GetComponent<T>() with your interface type (useful if you only expect ONE thing expressing that interface)
You can get ALL the MonoBehaviours as a list (with GetComponents<MonoBehaviour>() or even GetComponentsInChildren<MonoBehaviour>()), iterate them and ask if each one IS one of your interfaces, and operate upon it accordingly.
Here’s more info:
Using Interfaces in Unity3D:
Check Youtube for other tutorials about interfaces and working in Unity3D. It’s a pretty powerful combination.