I’m sorry, I misread your post. Mea Culpa.
So I guess you have no need to run to another church for RCIA…rather, send the kids running!
Seriously…you should discuss this with your priest, and if you get no results there, get ahold of your bishop. I have never heard of a “sealed envelope confession”, nor would I ever practice it.
Look at it this way…people in some countries or locations on this planet have no regular access to a priest so are unable to go to confession on a regular basis. If they die without the option of attending the sacrament of Confession, it is the intent that applies to the condition of their souls…if they intended to go to Confession as soon as possible, then a “state of grace” would be inferred, and of course only God could see that intent.
Under the “option” your clases have been presented, this emergency circumstance does not apply. If it were really an option approved by the Catholic Church, then what would stop the millions of people around the world from sending letters to the \vatican in sealed envelopes containing their Confessions?
This is not an approved method…see if there’s a shepherd around you who can make room in his pen for the new lambs.
Bless you for being a viligant watchdog to the shepherds!