Halvorsen and Molteberg

Am looking for information about my paternal grandmother's family. My great grandfather, Emil August Halvorsen, who was born in 1870, and baptized in Garnison Menighet, Oslo, Akershus, Norway, emigrated to the US, arriving in Boston, MA, in Sept. 1890. My great grandmother, Helga Molteberg (1870-1964) also emigrated to the US, and she and Emil were married in Worcester, MA, in 1891. I would like to know more about their antecedents, and perhaps learn whether there are any family members still living in the region of Oslo-Sarpsborg. Thanks in advance for any help that might be offered.