I would tell them the truth. Benedict XVI (and his immediate predecessors) are fallible human beings. However, we Catholics believe, on faith, that in essential matters defined in
Pastor Aeternus, an authentic Pope never errs. On the other hand, anyone can see, by examining the history of the Catholic Church, that many true popes erred in non-essential matters. So there is no problem to explain if you accept that Benedict is still and will be Pope until his death.
The usurper (Daniel 11:21) Cardinal Bergoglio is another matter. He is not actually the Pope, aka the Vicar of Christ. He is
the False Prophet. We are in "the end times," specifically the period called "the birth pangs" or "the beginning of the Sorrows" by Our Lord. The Bible and many approved prophecies have warned about this. St. Francis of Assisi, Quito, LaSalette, Leo XIII's St. Michael prayer, Fatima, Akita, etc. all specifically predict a period of apostasy at the
highest levels of the Church. That same apostasy was referred to by St. Paul in 2 Thessalonians 2, and it is happening now with Bergoglio.
The question of indefectibility does not come into play because there is still a Church with a visible, although impeded, head (Benedict XVI) and a mystical head (Jesus). The Church is still present, and will be until the end, in the faithful Remnant. In Zechariah 10, the prophet says:
2 For the idols have spoken what was unprofitable, and the diviners have seen a lie, and the dreamers have spoken vanity: they comforted in vain: therefore they were led away as a dock: they shall be afflicted, because they have no shepherd.
He is talking about the bishops leading the laity astray. There is no true shepherd because Benedict has been imprisoned and Bergoglio and his henchmen are destroyers of souls, as you will soon see with the upcoming Synod on Synodality. But clearly, this prophecy implies that "the Church" is going through difficulties near the end, just before Jesus comes back. "They shall be afflicted." The "they" are Catholics.
Bottom line: everything we are seeing was prophesied in the Bible. Get out of the weeds. Look at the big picture. Recognize where you are in salvation history. Again, if you haven't figured it out yet, you are in "the end times." All the prophecies will, most likely, play out within this decade. Do not fear. Love God and neighbor and utilize the Sacraments as long as they are available. They are likely to become scarce in the near future.