Me and my friend have started a band. We can play instruments. But we can't write lyrics. We're going post on YouTube. We'll gladly give you credit and we'll pay you if we make money.

This has been asked a number of times. No one here will write a song for you with the hope you will not only make money but will also pay the songwriter.

What you need to do is find songs you like and change them up -- make slow ones fast or fast ones slow, add riffs and sax/guitar/drum solos where they aren't any, add a descant, etc. Compare Susan Boyle's "Wild Horses" to the Rolling Stones' version to see what I mean.