Liam Aiken's birth name is Liam Padraic Aiken.
Liam Fountain's birth name is Christopher William Fountain.
I can find no canonized Catholic saint by the name of Liam.
Liam Gallagher's birth name is Gallagher, William John Paul.
Liam James' older brothers name is Sterling James.
Liam does not "mean" anything in Greek. Liam is a variant on the name William, which comes from Germanic roots meaning something like "resolute helmet" (or, figuratively, "guardian"). There are other languages in which a word similar to "liam" occurs, but as far as I know Greek is not one of them.
Liam Payne's first name is Liam.
Kieth. Liam Kieth Hemsworth.
Liam Hemsworth's full name is Liam Hemsworth. He does not have a middle name.
Conor Liam's birth name is Conor Liam Rasmussen.
Liam Macdonald's birth name is Liam Phillip Macdonald.
Liam Hooper's birth name is Liam Edward Hooper.
Liam Howell's birth name is Liam West Howell.
Liam Howlett's birth name is Liam Paris Howlett.
Liam Galvin's birth name is Liam Francis Galvin.
Liam Ferguson's birth name is Liam Richard Ferguson.
Liam Norberg's birth name is Magnus Liam Norberg.