In the past, some commentators argued that there is a distinction between the Philistine rulers and the Philistine commanders. In the context of the narrative itself however, it is clear that they are one and the same group of people and there is no need to distinguish between them.
6 Then Achish called David and said to him, “As the LORD lives, you have been honest, and to me it seems right that you should march out and in with me in the campaign. For I have found nothing wrong in you from the day of your coming to me to this day. Nevertheless, the lords do not approve of you.