I think the problem is with the younger kitties...maybe THEY should have a vet checkup. I mean - what if they have their way with the older kitty and STILL have the same problem? I am thinking if you put to them the MONEY aspect - that they would then have extra vet bills, and it is more economical to get the young ones checked first, they might do that.

Considering they don't 'listen to reason', they might listen to the money/hassle of extra vet trips perspective.