If you use lyrics from Child's set of Popular Ballads you should not have copyright worries.   While I am not an expert on copyright law, I would think that anyone who may have applied for a copyright for words identical to a ballad in the Child collection would have a difficult time proving ownership in court.

Lowlands of Holland should make an interesting subject. Here in the Ozarks there is a version called Lily of Arkansas that was collected by Vance Randolph and recorded by Cathy Barton and Dave Para.

Are you acquainted with Charles Vess' series of illustrated ballads? He covered Tam Lin, Barbara Allen, King Henry and others. He originally published in the comic book format but the series is now available in one set. You might want to stay away from his subjects. You should also be able to copyright your work. While you could not claim ownership when someone sings or records the ballad you would have recourse if someone were to make unauthorized use of the drawings.

Charles Vess