Please. It’s got nothing to do with Ga’ava. It’s called boredom. And yes, it is rude.
Sacrilege, your case is not just boredom; it sounds like what you describe it as – misplaced Hasmada. If these family members are in sphere of influence, you can point out that you’ll never see an Adam Gadol learning from a Sefer by a Simcha. If they really want to emulate Gedolim, they can speak Torah to each other and to the family.