Some of this is open to interpretation:

The official word in recorded history is that Alma and Ramza were killed in the final battle against Altima, as apparently were everyone else in Ramza's party. Orlandu of course died earlier, in Bethla Garrison (in reality his double). His contributions to saving Ivalice were lost to history, with the credit going to Delita.

This is why they were in attendence at their own funeral. Olan witnessed that they were alive and well, which was instrumental in his descision to write a revisionist history of Ivalice. Naturally he was silenced by those in authority since it cast such a dim view of the Glabados church and the ruling king, Delita. It took decades before Olan's decendant Alazam was able to tell the true story, which is the story of FFT.

Ramza was truly selfless and apparently okay with the idea that his hard work was not recognized. He's one of the few characters that seems to beleieve in virtue as it's own reward. In order to preserve the official story, he had to pretend to be dead. Perhaps also it gave him and his sister a rare oppurtunity to start over and free themselves from the society of Ivalice.

As for Delita and Ovelia's fate, it boiled down to Delita's lies and deceptions coming back to haunt him. He had shamelessly used Ovelia along with many of his friends and enemies, but she didn't know how much he had betrayed her trust until up to right before that moment.

Consider that he murdered his own leige, Goltana, along with two of his closest advisors. He also cut out Balmafuda's tongue. Ovelia had a right to be worried.

I suspect Ovelia perished from their scuffle and Delita survived and went on to reign as the 'elightened king' that mainstream history has portrayed him as.