UK Home Office will be more interested in proving that both of them have strong ties to the Philippines and will not overstay in the UK. You need to gather evidences for that, i.e. properties, work, etc. if they do have them. On your part, you only have to supply documents that you really can support them while they're here, i.e. accommodation (that you have room(s) for them if they are staying in your house), your bank account(s) showing you can really afford it, also provide a cover letter for the application stating what they are going to do in the UK and you are fully supporting their stay. The hardest part really is proving and convincing UK Home Office that they'll go back to the Philippines.