are they filipinos also? it'snice to ask the would be bride and groom for whatever they would like so at least the song has some meaning for them but anyway in general all wedding songs are really nice nd touching.
some of my suggestions would be:
if tagalog:
1. ikaw - pretty old and common but really really nice
2. sa piling mo - good lyrics
3. pangarap ko ang ibigin ka

english ones:
1. the prayer - good song for preparatories and prayer stuff
2. i will be here - excellent melody and lyrics too, of course (we did this with my bro, instrumental, wow, it was amazing?)
3. i finally found someone
4. thank god i found you
----if you are doing duets...
5. love will be our home - a christian song
6. just at the right time - love this one, tho its not common tho, i had to get my own band for this when i sang it
..... and a whole lot more.............

it really just depends on what you like and feel like singing and what message you want to get across to them.
its always a pleasure to be asked to sing in ceremonies like this. go girl.....

“A friend is one who believes in you when you have ceased to believe in yourself.”