The nursery rhyme never explicitly states whether they are siblings, but it was based on the myth of Hjúki and Bil, who were siblings. In the original the brother and sister were captured by Mani (the moon god) and taken to the moon, while fetching a pail of water from a well.
Who is the Mexican Grandma in Jack and Jill?
Eugenio Derbez: Felipe, Felipe’s Grandma.