@WatchMaker It doesn't actually get bad after this part specifically, it's only with Cold Steel that it actually gets bad from then on. That said, if you're specifically wanting to follow Joshua and Estelle's stories to see what happens to them after that (along with the Sky cast in general), you'll be fine for the next 3 games or so, aka Trails in the Sky 3rd and the Crossbell duo, up until the Cold Steel arc (granted, other characters will take the helm as the main characters after this game, you'll just get updates about the Sky gang here and there). Cold Steel is when they disappear as a main focus of the series for the most part (another reason that Arc sucks, among many other reasons in terms of bad pacing and fanservice garbage, and so on). So just a heads up there.

That said, I will say that despite the misgivings of the later games, the Sky characters when they are around are never handled poorly thankfully, they're always done justice. It's just everything around them plot wise starts going to crap lol.