This could be a long process.
I think Phase 1 of the subpoenas is focusing on getting records rather than on getting testimony from elders and ex-elders.
Once the Attorney General's staff goes through those records and identifies situations where the elders did nothing or covered up abuse then will come Phase 2 where they will have questions prepared for elders and ex-elders regarding what they did or didn't do, what COs or the Branch advised them to do, etc.