Sorry about the delay on an answer for this
I was able to research a bit and here is what I found
CLICKH HERE for a site that discusses requirements
Unfortunately the main one that will impact him is the 10 year legal residence requirement (especially at his age). Most countries have this type of requirement, however. Even with marriage it would take time for it to occur (and cannot find for sure if would be under 10 years still or not - I think 10 years is still required).
CLICK HERE for a direct link to the phillipines government website with more information that might help as he begins this journey.
I hope this helps. I wish your brother in law all the best as he takes this next step in his life.. how exciting.
I will request - however, be sure to rate my response if you were satisfied as that is the only way that I receive any credit for my help today.
All the best to you and your brother in law