Were they just sort of the normal people inhabiting the land intermingling with the local inhabitants after?

Yep, pretty much. They seem to have set up kingdoms and settlements in the Levant and blended with the native populations. As a recent study put it,

Our analysis suggests that this genetic distinction is due to a European-related gene flow introduced in Ashkelon during either the end of the Bronze Age or the beginning of the Iron Age. This timing is in accord with estimates of the Philistines arrival to the coast of the Levant, based on archeological and textual records. We find that, within no more than two centuries, this genetic footprint introduced during the early Iron Age is no longer detectable and seems to be diluted by a local Levantine-related gene pool.

I touched on Philistine settlements and archaeology in Tell me about the Philistines vs others in the Levant 1200 to 800 BCE and the probable Aegean origins of a kingdom in Cilicia in Karatepe and Çineköy inscriptions: Luwian and Phoenician and Sea Peoples.