Our dad's parents were Gustave Martens and Margaret Bischoff of College Point, NY.
The Martens Bischoff families both emigrated from Germany in the 19th century and settled in Brooklyn and Queens.
The earliest known record of the Martens Family shows that in 1850, five brothers from the Kingdom of Hannover arrived in New York City. (Germany was not unified as a nation until 1871). One of the brothers, my great-great-great-grandfather Diedrich Martens, was naturalized as a U.S. citizen on October 8, 1855.
As for the Bischoffs, much of my information on them focuses on the maternal side:

Margaret Bischoff's maternal grandparents,
Barbara Cordier and Adam Kuntz.

Barbara as seen in Gustave's home movie circa 1931.
She lived for at least another 20 years and died in her nineties.
Barbara Cordier-Kuntz was born in Germany in the 1860's,
and although she moved to America as a young woman and remained there for the
rest of her long life,
she never learned to speak English.
Her ancestors were originally French Protestants or "Hugonauts" who
had emigrated to Germany
from predominently Catholic France to escape persecution.
To her grandchildren she was "Grossey," derived from Grossmutter,
the German word for grandmother.

Barbara's daughter Katharina "Kitty" Kuntz married Frederick Bischoff,
son of Anton Bischoff and Lisbeth Hoffman.
Kitty died young, of a heart attack, in 1932. She was only in her forties.

During the Great Depression, Fred Bischoff worked as a butcher at Schafer's
Market in Manhattan.

Schafer's Market at Christmas time, 1926

Kitty and Fred's daughter, Margaret Bischoff (our grandma) as a young girl at
PS127 (now demolished).
Click the classroom to embiggen

Margaret Bischoff's sister, Eleanor, in the 1920's.

Margaret Bischoff, sometime and someplace in the 1920's.

4 generations, left to right: Barbara "Grossey" Kuntz, Katharina "Kitty"
Kuntz, Margaret Bischoff,
and Margaret's son Warren, our father. From 1931.

Margaret Bischoff's future husband, Gustave Martens of Whitestone.

Uh oh, here's the man who almost married Margaret Bischoff!
Jack Case played in Gustave Martens' party band Martens' Peerless Orchestra.
Jack and Gus must have remained on good terms after the marriage,
or else this picture would not have remained in Gus and Margaret's collection.

In the late 1920's, newlyweds Gustave and Margaret moved into this College Point
house
and stayed there for the rest of their lives (how different that is from today!)
Margaret's sister Eleanor and her husband Matthias Schreiner
moved into the upstairs apartment and likewise stayed there for good.

Margaret in the 1940's. Gustave had sold the car
and used some of the money to buy the nifty
radio and record player combo that Marg is enjoying.

Peek a boo!

Friends of Gus and Margaret, starting from the top:
Percy Simpson, who played piano in Martens' Peerless Orchestra.
Jayne Simpson, Percy's daughter.
Percy's wife, Carrie.
At the bottom is Carrie's mother "Ma Case", who was also the mother
of Jack Case,
the violinst who almost stole Margaret away from Gustave!

The man in white is Gustave's Uncle Will -William C. Martens.
Uncle Will's keg parties were an annual tradition.
The young fellow second from left is William's son, Fred "Spike" Martens.
Spike later became an Ob/Gyn physician in Manhattan.

I will always remember Gustave and Margaret as "Grandpa and Grandma,"
and this is my favorite photo of them.
Gustave passed away in 1977, and Margaret in 1981.
Their ashes are interred in Flushing Cemetary, NY.
Here are some curious and unidentified photos from their collection:

The unnamed kid at right is dressed as a member of the Masonic Junior League.
Whether or not he was related to Gustave who was also a Mason, or perhaps
is Gustave, I can only guess.