How to Play sequentially more than one AudioSource in one game object ?

Here is a class that will allow you to do just that. It has two public lists, one is of the AudioClips and the other is for the AudioSources.

The class is flexible in that the only main requirement is that you have to set the AudioClip list soundList . This can be set to as many AudioClips as you want, it is not limited to three.

This class could also be modified to use just one AudioSource. Is there any reason why you need more than one?

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 public class AudioManager : MonoBehaviour
 {
     [Tooltip("List of AudioClip components. This list must be set to the sounds to be played and in the order of the list.")]
     public List<AudioClip> soundList = new List<AudioClip>();
 
     [Tooltip("List of AudioSource components. This list does not need to be set.")]
     public List<AudioSource> audioSourceList = new List<AudioSource>();
     
     [Tooltip("This variriable resets the audioSourceList and creates a separate AudioSource for each clip if set to true.")]
     public bool restAudioSourceList = false;
     
     [Tooltip("AudioSource default. Only used if AudioSource is created at runtime.")]
     public bool playOnAwake = false;
 
     [Tooltip("AudioSource default. Only used if AudioSource is created at runtime.")]
     public bool loop = false;
 
     private bool soundsGoodToPlay = false;
     
     void Start ()
     {
         if (soundList.Count > 0)
         {
             // this loop just make sure that there are valid AudioClips in the soundList
             for (int i = (soundList.Count - 1); i >= 0; i--)
             {
                 if (soundList[i] == null)
                 {
                     soundList.RemoveAt(i);
                 }
             }
             
             if (soundList.Count > 0)
             {
                 if ((restAudioSourceList) || (audioSourceList.Count == 0) || (audioSourceList.Count < soundList.Count))
                 {
                     audioSourceList.Clear();
                     for (int i = 0; i < soundList.Count; i++)
                     {
                         AudioSource source = gameObject.AddComponent<AudioSource>();
                         source.playOnAwake = playOnAwake;
                         source.loop = loop;
                         audioSourceList.Add(source);
                     }
                 }
                 soundsGoodToPlay = (soundList.Count > 0);
             }
         }
     }
 
     void PlaySequentialSounds()
     {
         StartCoroutine(PlaySounds());
     }
 
     IEnumerator PlaySounds()
     {
         if (soundList.Count > 0)
         {
             for (int i = 0; i < soundList.Count; i++)
             {
                 audioSourceList[i].PlayOneShot(soundList[i]);
 
                 // wait for the lenght of the clip to finish playing
                 yield return new WaitForSeconds(soundList[i].length);
             }
         }
         yield return null;
     }
 }

The following class does the same as the one above but uses only one AudioSource

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 public class AudioManager : MonoBehaviour
 {
     [Tooltip("List of AudioClip components. This list must be set to the sounds to be played and in the order of the list.")]
     public List<AudioClip> soundList = new List<AudioClip>();
 
     [Tooltip("The AudioSource component to play the AudioClips.")]
     public AudioSource audioSource;
     
     [Tooltip("AudioSource default. Only used if AudioSource is created at runtime.")]
     public bool playOnAwake = false;
 
     [Tooltip("AudioSource default. Only used if AudioSource is created at runtime.")]
     public bool loop = false;
 
     private bool soundsGoodToPlay = false;
     
     void Start ()
     {
         // make sure we have a reference to the AudioSource
         if (audioSource == null)
         {
             if (audioSource == null)
             {
                 audioSource = gameObject.AddComponent<AudioSource>();
             }
             else
             {
                 audioSource = gameObject.GetComponent<AudioSource>();
             }
         }
         audioSource.playOnAwake = playOnAwake;
         audioSource.loop = loop;
 
         // this loop just make sure that alll the AudioClips in the soundList are valid
         for (int i = (soundList.Count - 1); i >= 0; i--)
         {
             if (soundList[i] == null)
             {
                 soundList.RemoveAt(i);
             }
         }
     }
 
     void PlaySequentialSounds()
     {
         StartCoroutine(PlaySounds());
     }
 
     IEnumerator PlaySounds()
     {
         if (soundList.Count > 0)
         {
             for (int i = 0; i < soundList.Count; i++)
             {
                 audioSource.PlayOneShot(soundList[i]);
 
                 // wait for the lenght of the clip to finish playing
                 yield return new WaitForSeconds(soundList[i].length);
             }
         }
         yield return null;
     }
 }