Very simply put..... Tagalog or local variations of it are the national language of the Philippines period. English is taught as a second language period.
I think it very sad to think that any child born of mixed parents ie: fil/brit will not learn and be able to communicate in both tongues. I am dead sure my little son with be learning both and be able to communicate properly in both. Both my wife and I will make sure of that.
You did mention about Manx being lost over a hundred years ago, well, that was then, but in this case we are talking current taught national language.