The Maharlika were actually a martial class of the Tagalog people. It wasn’t a kingdom. They sort of a lower level nobility (they were an upper warrior group but may have enjoyed higher standing by marrying into the royal class, the Maginoo, which would include the Datu among others). Honestly, there isn’t a lot to say about this group, and the history surrounding them is a bit thin. William Henry Scott and Samuel K. Tan have both discussed them in scholarly works, but most scholarship of Tagalog society centers on different areas. I’m giving a short answer now because it is late at night, but I can add on to this post tomorrow (if that is okay with the mods).

I will provide some sources for you to check out though (these definitely can be found in the Philippines too, if this question is coming from there):

Barangay: Sixteenth Century Philippine Culture and Society by William Henry Scott

A History of the Philippines by Samuel K. Tan

Honestly, my favorite source to cite for precolonial Philippine societies tends to be by the archaeologist Laura Lee Junker. It sheds the reliance on Spanish and Chinese histories (Philippine writings did not preserve well). Her book:

Raiding, Trading, and Feasting: The Political Economy of Philippine Chiefdoms

is absolutely essential reading in this area of study.