For your first question, you should look for a copy of Raiding, Trading, and Feasting: The Political Economy of Philippine Chiefdoms by Laura Lee Junker. This book discusses exactly what you want.

For Philippine languages, I can tell you that they are Austronesian languages in the Malayo-Polynesian subfamily. They have the same Proto-Austronesian origin as languages such as Malay and Hawaiian and Cham, among many others. Philippine languages in many ways are actually quite informative in the reconstruction of the proto-Austronesian language since they retain many of the features that other languages in the family such as the ones in Indonesia lost over time (in this regard Philippine languages are nearly unique in fact). The Austronesian family was the most widespread language family in the world prior to the era of European colonialism, stretching from Madagascar through Maritime Southeast Asia and on all the way to Rapa Nui, which is near South America.

As for writing, the Philippines did indeed have its own writing systems prior to Spanish arrival. In fact, the Spanish claimed that few Filipinos were illiterate in the writing systems, and among Filipinos the most literate were the women. This makes sense when one considers the way precolonial Filipino societies were structured. The problem with preservation though is that Filipinos did not write on paper (and even if they did, paper doesn’t preserve well in the tropics); instead the writing was done on bamboo, which of course did not last. Some writing has survived though, such as the Laguna Copperplate. The Spanish did actively attempt to destroy Filipino culture (not that it was actually successful, since indigenous Filipino culture remains even if many may not recognize it as such immediately) including destroying Muslim temples/mosques in the islands. A good source for understanding indigenous Philippine writing systems is the book 3 Baybayin Studies by Ramon Guillermo et al. There they break down exactly how the writing systems may have been utilized by the women in society (as most users of it were women), as well as the systems’ history in the islands.

If you would like me to discuss precolonial Philippine societies, I would be happy to in a followup.