1) Grandpa doesn't think Elly is being rude or interfering or insensitive. He thanks her for meddling in his plans for his Final Rest.
2) Elly castigates Grandpa for using an "indelicate" euphemism like "pop off." How is that offensive, exactly? I suppose the only appropriate ways to refer to the death state are those euphemisms that are so vague that they confuse some people as to what you're talking about.
3) Grandpa doesn't think it's offensive that Elly didn't invite Iris, or give him time alone to discuss this with Iris. In fact, as the hulking shadow in the doorway in Panel 4 proves, Iris is not even allowed to be in the room when this discussion takes place. Grandpa decides to divide his ashes--AND DECIDES THAT IRIS WILL DIVIDE HERS TOO, BY GOD!!--and that half of them will rest together next to Smelly Elly.
4) Then Grandpa concludes the strip by saying that he will go TELL his spouse what he has decided about the disposition of their final remains. Does this treatment of his spouse look familiar? Yes! This is how Elly treats John all the time! I hope Iris knows that she's not supposed to have an opinion about this! Really, it would be perfectly reasonable for her to feel that no, she'd rather go be buried in her entirety next to her first husband and kids, but if she feels that way, it doesn't matter to Grandpa. A RICHARDS' WORD IS LAW!
All of which leads me to wonder: suppose tomorrow, Elly is driving Grandpa to the dentist, and they're T-boned by a bus, thus eliminating the Richardses from the strip. Would John, Iris, and April heave a sigh of relief and turn into normal people? (I have no hope for Mike and Liz, they seem thoroughly Richardsized to me.) I mean, the puns would no doubt remain, but would they be less holier-than-thou?
I picture Iris moving into the Patterson homestead, and the three of them living in harmony. Iris laughs it off when the dog soils the floor, or when John folds the towels wrong. John shakes off his relentless obsession with trains and starts dating Beatrice Alfarero--the only single woman in town--and they laugh all day long over their respective "Elly Stories." April gets lunch money for chicken wraps as a matter of course and is allowed to get a decent haircut, sans bun. The whole last year of the strip could be devoted to showing how the way Elly and Grandpa acted really was tremendously FLAWED.
Of course, that will never happen. Because it would be AWESOME.