Everyone is responsible for ALL of the code.
Tough but the only practical thing to do!
This means that everyone must have confidence in every member of the greater team.
But it also means that any pair can change any code.
This requires strong focus that the FACE of every object is well-defined with Pre- and Post-assertions for every method.
The Build must be able to be run by each Pair with standard testing databases. Pairs do have to be aware that multiple changes to common code can give conflicts in the build.
The Standards will have to cover style and “pretty-print” conventions (or tools).