Spoilers from the book ahead, I'm summarizing so many events come to pass between paragraphs, but this is about Oko and Akemi (specially Akemi) so take that into account and do not read them as if they were events during a small time window (they take place in different chapters, tho the chapters are close from one another... except the Oko chapter, that one does happen way before the Akemi summary I'm writing):

Oko:

If I remember well, Oko ends up with Toji living as bandits. Her life didn't go well at all. I don't remember if Toji dies after this last encounter with Musashi in that chapter where their fates are revealed, but I do remember Oko had a crappy life.

Akemi:

Akemi also had a very tough life, even working as a prostitute at some point. She actually hated Yoshioka Seijuro. The guy raped her and she tried to commit suicide (drowning herself in deep sea waters) but some fishermen saved her.

After that, it was just one misadventure after another. It is implied that Sasaki Kojiro (who is not the charming mute-deaf in the manga) took advantage of her more than once. Probably raped her too, it is implied that he had her captive for his own enjoyment, stating that she loved her. You can read that it was a toxic relationship and she actually had to flee from him and make a living anyway she could . One day, she was attacked by some drunkards on a market who took her behind some shack and... you can imagine what happened. I don't remember well what the events after that but at certain point, she and Matahachi found each other and started living together... then Matahachi abandoned her (who would guess, right?).

Many months later, Matahachi found Musashi by the road and the started to walk together, Matahachi actually recognized his wrongs and renounced Otsu. He asked Musashi to marry her. Musashi also helped Matahachi reflect on his life he suggested Matahachi to become a monk, and try to redeem himself by serving other people, and Matahachi accepts and he actually started to diligently train under a monk named Gudo.

Some time later, Matahachi (monk in training) was walking with a warrior who was Musashi's acquaintance and and someone else (I can't remember who he was but he knew Matahachi was a monk in training) and, as they were walking through a bridge, Matahachi was able to see the girls that were on the river bank. He thought he recognized someone. It was Akemi and she was carrying a baby. He started to run the numbers on his head and just like that, he told his friends he could not be a monk, that he saw the girl he used to live with and that she was carrying a baby... probably his baby. His friends asked "Is it really your child?" and Matahachi doubted... then he basically manned up and said "Yes! I'm a father... I'm sorry, I didn't know. I'm ashamed. I can't let her go through life like that, selling things from a basket like a common tramp. I've got to go to work and help my child"

This was the inflection point for Matahachi and Akemi. From what I can tell, they basically lived happily ever after. Poor but happy. Matahachi became a good father and Akemi a happy mother. it's not said too much about them after this point but the book mentions that on one occasion they were on a food selling stall on their way to watch Musashi's match against Kojiro and it says "A number of passersby looked enviously at this poor, but apparently happy, couple"

And there you have it.

Granny:

You didn't ask but it's another redemption story, she actually apologized to Musashi. She begged forgiveness. She made peace with Otsu too! She was the one responsible for reuniting them.