“Ha, these two were deeply in love and had a marriage stronger than money! What losers!” Fairly hard to make the claim the joke is at their expense.

This might be a language thing though? The phrase at their expense tends to mean that whomever is the butt of the joke. In this case, the four audience marriages are the butt of the joke as they are not as in love as the deceased.

I don’t know if you’re old enough to have spoken at funerals. There are jokes you tell while doing so, usually framed like this wherein you’re praising the deceased (usually a common memory, like their cooking) and comparing yourself or the crowd unfavourably.

Now, I’m not sure it was appropriate or wise for trump to try this at a fundraiser but it seems disingenuous to say he was making fun of the deceased, which is how most English readers would interpret the headline.