I've seen the term "redundant knights". In general, redundant pieces are pieces can get in each other's way. Here's a quote I could find about the general principle, but not specifically about knights:
Interestingly, two of Lasker’s other points were:
• The principle of
redundancy: Two pieces that move the same way on the same squares can
easily get in each other’s way, while two pieces that never get in
each other’s way – like two bishops – are better coordinated. This was
verified by computer analysis by Larry Kaufman 60 years later! Larry’s
important contributions are noted in several places in this book.
Heisman, Dan. Elements of Positional Evaluation (Kindle Locations 1035-1039). SCB Distributors. Kindle Edition.
Googling specifically for "redundant knights" I found this (also by Dan Heisman):
For example, he calls two knights that guard each other “redundant knights” and notes that this is usually a weak setup.
I don't have access to that article as I'm not a chesscafe.com member so I don't even know who "he" is (maybe Lasker or Kaufman?), so if anyone with full access to that article can provide more context, I'll happily edit my answer.