Did Saints Peter and Paul believe in insider movements?

I answer that the Biblical witness clearly leads to the answer no:

Further, the mixed churches in cities like Rome and [the region of] Galatia were likewise errors. These believers, both Jews and non-Jews, had mistakenly supposed that they in some way had come into a new oikos and a new identity, and Paul, lacking wisdom as usual, taught them these things. Indeed, a triumph of IM hermeneutics and practice would have meant that Peter should have been victorious when Paul confronted him. Indeed, Paul, in violating kashrut was stepping needlessly outside of his oikos, while Peter himself was honoring his God-given identity as a Galilean Jew. 

In the end though, it was the faith—the apostolic faith—that was victorious. A faith which understood that in Jesus a new community had come into being demanded allegiance above and beyond one’s own community of birth. Or as one African pastor put it in those early centuries: you cannot have God for your Father without having the Church for your mother.

From my recent article on insider movements.