They might, at least, be 'optimistic'!
There's no legal obligation upon someone who arranges a funeral to follow any instructions left by the deceased. Putting "I wish to be buried next to my wife in St Mary's cemetery, Glossop" doesn't prevent the person arranging your funeral from seeing you cremated in Gloucester.
The 'instructions' in my will (which, as I've stated, can really be no more than 'wishes' anyway) have absolutely nothing to do with conceit or vanity. They're simply practical. (Quote: "I desire that my body be cremated without ceremony and that my ashes be disposed of, also without ceremony, in any convenient refuse receptacle").