Well, you do raise an issue that can be more of a problem within Lds facilities for any gatherings.
If you look @ any given Lds parking lot, you will see more vans & other high-capacity passenger vehicles.
Larger families can make it more difficult to simply "squeeze" in where you can if you arrive "later" to a service/event.
Naturally, some larger families become turf-protective for this simple reason.
(Obviously, it didn't seem to readily apply to the perp in this situation)
There is no reserved seating unless the church says so. The “regular” did nothing wrong by sitting in the middle of an out of town family.
We call them MAVs - Mormon Assault Vehicles. One pulls up, to doors slide open, and out pops 8 mormons.
Being out-familied, I backed down right quick.
"Ok, ok lady. It's your pew". no problem lol -- "but why do ya'll sit in the back corner? I'm just try to sneak in and not be noticed."
slinking away, muttering maybe I'll make it out of here before anybody offers me a visitor's card [grin]