To me, this is a wild mix of two companies because the last name of the founders are the same.
(In such a case, I would also be a famous pianist and would make shoes and produce documentaries etc - nope

)
www.datamp.org ... Eugen Zerver / ZEREM Remscheid-
"The Zerver family has operated the company for over 150 years;"
The ZEREM company as far as I know only 40-50 years - I suspect they only existed until the '60s.
This is correct for HAZET - founded in 1868 by "Hermann Zerver" - a different company.
"in the 21st Century the company uses the HAZET brand name."
definitely not... also since the early 20th century.
HA-ZET (as the first letters H & Z pronounced in German of Hermann Zerver, born 1840) was registered in 1913 and used till today.
HAZET has some other sub-brands as VIGOR or used the yellow HAZET Standard series for cheaper tools in the '70s.
The family of Hermann Zerver is somehow known till back to 1585 and the family name changed step by step from Zörb to Zerver.
Eugen Zerver (born 1897) was not mentioned in the HAZET chronicle or this Hermann Zerver family — nor was his company ZEREM. He was apparently active before and after WWII. Apparently mainly pliers. Perhaps he, like other companies as Stahlwille or Belzer and others, manufactured tools for HAZET.
Keep in mind the German city and region around Remscheid and Wuppertal have till today a lot of well known old tool brands.
(Knipex, Wera, Picard, Stahlwille, GEDORE, DOWIDAT, Belzer, ...). So what will you do if you were born in the region during this time...
regards,