Will the Freys give up their hostages?

[Runaway Penguin]

They didn't release them to KL, or Kevan's Epilogue would mention the party underway. It is doubtful KL knows or cares about it.

On the other hand... If UnCat tries to use the prisoners as one of the reasons why to hang Jaime and he gets convincing enough flash of anger... ;) I can see his knowledge of the prisoner situation to be one of his bargaining chips. After all, he tries to prove he has some honor at least and definitely won't want to be the fall guy for Freys.

Late Lord Walder doesn't probably care too much about Lannisters, TBH. Esp. without Tywin and Kevan. I can see a lot of things... Like Freys trying to kill Edmure by attacking him as he is escorted to Casterly Rock. And wouldn't that be sweet? BwB rescue party having to join forces with the Lannister escort to fight off the Freys?

[IRON BANK]

They will release the prisoners because they are truly believing that they are winning and that this is just a soldification of their authority. On the way the to KL prisoners will be freed.

[Runaway Penguin]

They believe no such thing and they didn't like much Jaime ordering the transfer. They will try to hang on to them.

[Faint]

If we assume this timeline is roughly accurate, it has been about a month since Jaime ordered the hostages released to King's Landing, yet Kevan nor anybody else makes mention of them in the epilogue of A Dance with Dragons. That is why I have my doubts over whether the order was ever carried out. We also have to consider that Jaime went missing only a week or so after telling the Freys to release the hostages.