There is a lot here that i don't know the answer to but here are my thoughts.
1. Paul can be very blunt when he wants to.. to imply that he was subtilling jabbing james is uncharacteristic of his treatment of Peter and others.
2. Neither james nor Paul were the original 12 apostles. They were both apostles in the sense that they both met jesus and were called to the office. James was more than an apostle. He was head of the church and jesus brother.
3. Paul was a missionary to the gentiles. Peter was to the jews. They were both trying to bring people to the messiah in different target markets
It was determined by James at the council the requirements to gentiles as more limited. This is based on leviticus 17. While paul desired to increase the commonness among the two groups, there were customary differences. James, as well as Paul, had to deal with the differences. My Interpretation of "from james" implied Jewish Christians from James church which had different cultural needs.
Im still.learning about circumcision in second temple judism. This article i found interesting
https://www.jewishencyclopedia.com/arti ... rcumcision
"The issue between the Zealot and Liberal parties regarding the circumcision of proselytes remained an open one in tannaitic times; R. Joshua asserting that the bath, or baptismal rite, rendered a person a full proselyte without circumcision, as Israel, when receiving the Law, required no initiation other than the purificative bath; while R. Eliezer makes circumcision a condition for the admission ofa proselyte, and declares the baptismal rite to be of no consequence"
Possibly there were Jewish Christian zealots who believed in circumcision of gentiles. If so, while james does not attack them. His decree for gentile twice does not make circumcision mandatory and the gospel message clearly focuses on baptism.