It’s going to be interesting to watch when HW Bush and Jimmy Carter die.
The Clintons at least got to be pretty close to the Bush family, and I think the Obamas got along with them as well. Carter's a Democrat so if anyone avoids that funeral I'd think it would be the President.
There is no love lost between Trump and the Obamas or Trump and Hillary. Franklin Graham's a birther who claimed Obama was a Muslim. I'd love to be a fly on the wall on the slim chance those two ever meet again. So the story isn't that neither are coming. The story would be if either one did.