The questions at the end are so misleading and twisted. It reads like an examination of conscience.
For example, the first one. The Church can never cease being the true church of Christ or it would no longer be the Church. However, a counterfeit church can exist, and individual members can fall away from the Church by apostatizing and rejecting the truth. Also non members of the Church can fake membership and hold key positions in Rome, yes. By their fruits you know them, said Christ.
You cannot make an act of Faith and then join a false conciliar church which is anti-Christ. You become a contradiction. That's what the FSSP is.