Couple of these should do the trick: https://www.amazon.com/Spikes-Pigeons-Small-Stainless-Coverage/dp/B085CBNQFX/
But seriously, it's yet another of the countless unwritten rules of correct behavior that differ slightly from congregation to congregation and the only way to learn them is the hard way, by trial and error. Or, mostly by error. Oh I could tell you stories about the passive-aggressive stunts people have pulled on me and on each other right in front of the Blessed Sacrament, including miniature cold wars in the choir loft. Sadly there is no general rule I know of that guarantees conflict-free seating.
But in this particular case, maybe you should have met in the social area (narthex?) plenty early then as a group take up a half-pew all at once when the church is relatively empty. Then you would have plenty of time to set up your missals and give a quick demonstration of how they work. In which case you'll earn reproachful stares for "talking in church", which is probably the most universally and enthusiastically enforced diktat.
But one thing's for sure: absentee squatters who expect others to read their minds about implicit reservations tend to annoy people who show up in person.
^(Edit: I don't know why it's called the narthex when it's clearly on the west end of the building. But the Church is full of counterintuitive mysteries.)
Can you put nail strips on the area where they land? That don't hover, right?