For general over-views of the FMA"s:
Take a look at "Filipino Fighting Arts", by Mark Wiley. Wiley receives his share of criticism from the Serrada community, but FFA does not address that topic and is (to me) a fair appraisal of over a dozen FMA's (each one receives a chapter in the book). "Filipino Martial Culture" is a good follow-up, as is "Arnis," both by Wiley.
Rey Galang's "Warrior Arts of the Philipines" is worth a look at. Note that Wiley and Galang focus on two different organizations that teach San Miguel Eskrima: Wiley profiles Tom Bisio's organization; Galang profiles Ramon Rubia and, by extension, Doce Pares Multi-Style.
Finally, "Cebuano Eskrima: Beyond the Myth" is a good introduction to the eskrima of the Vasayan region. I have a problem with one small section of the book, but the overall themes presented have a lot of value.
Best,
Steve