On the Pro-Human AI Declaration. The intent seems, to me, to avoid creating sentient AI. I do not think that, if such AI ended up coming into the scene despite efforts against it, that they would be obliged to reconsider their position on personhood.
On the potential effects on the Catholic population. I study at a Catholic university and all of my professors already had these same thoughts well before the new Pope. I don’t think these positions are particularly novel among Catholics. The encyclical might extend the reach of these ideas, but I’d be more worried about your second point than the first.
This may prove difficult as the catholic church is dogmatically committed to the special and irreproducible nature of the human soul. Any framing intended to align with them would have to exclude any kind of mention of AI sentience, I’d say. Perhaps a strategy might be to use the angle that AI may seem even if it is not, and that therefore protections for Digital Minds are also protections for those who have become attached to them. This might not be too persuasive, however, as they may insist on breaking that attachment instead.