Nope the 757 was a replacement for the 727-200. Early studies even proposed keeping the T-tail.
The 767 was not so much a replacement as a design leveraged off the same wings and systems with a wider cabin. You might loosely say it was a 707 replacement, but I don't recall it being stated as that.
ETOPS and two pilot crews were all new innovations. In the early years half the world's ETOPS experience on the 767 was amassed between New Zealand and Australia by Qantas and Air New Zealand.
The 757 however was always promoted as the 727 replacement. Not a 737 replacement. The 737-800/900 many years later grew into the 757-200 niche.