Hi! I'm Filpina too,
You can start by checking the website of ICAB (Inter Country Adoption Board), and you can email them your intention to adopt your wife children.
Ask them if by going back to the Phils will have more positive outcome to do the adoption or here in the states.
www.skyinet.net/~icaba/
you can also check these:
www.bcis.gov , go to the link naturalization, then, inter-country adoption
www.immigration.gov.ph
www.ohiohomestudy.com and
www.1800homestudy.com (just to have an idea what is homestudy)
Good Luck