My great great grandmother was Hortensia Grau y Batlle (Juana Díaz, P.R., 1842- Sarrià, Catalonia, 1913) who married my great great grandparent Simon Pierluisi y Pierluisi (Sisco, Corsica 1832-Barcelona, 1896). She had a sister called María Grau y Batlle (born in Juana Díaz, 1857) who married Oscar Schuck y Oliveras or Olivera (1850-1931) in 22 Apr 1878 (Nuestra Señora de la Guadalupe, Ponce).
Oscar Shuck was son of Felipe Schuck y Schurer, shoemaker (born in 1827), who married Josefa Olivera y Aravi (born in 1827). They had two sons: Eseac (Isaac?, born in 1847) and Guillermo, your grandfather (born in 1849). Felipe Schuck, his wife and sons were living in Ponce in 1860.
The first marriage of Oscar Schuck y Oliveras was in 18 Jun 1873. He married Dolores Cabrera in the Cathedral of Ponce.
Maria Grau and Oscar Schuck had six sons:
Guillermo (Ponce, 1881) María (Ponce, 1882) Pedro (Ponce, 1883) Enrique (Ponce, 1884) Luisa (Ponce, 10 Oct 1885-Sep 1979) Horacio (Ponce, 1888)
The most important part of this information comes from prof. Licy Tomasini who is studying the registers of the Cathedral of Ponce and the Archivo Histórico de Ponce.
I have some data from the descendants of the Schuck-Grau brothers. I will send it to you if you want them.