I would load the ISO in a software like DVD Shrink or DVD Rebuilder, blank half of the episodes, export it and create a new ISO from that. Then repeat the process but with the other half of the episodes blanked. Maybe you also need to blank some extras or remove superfluous audio tracks, compress menu etc. to make them small enough because half of episodes + menus/extras plus half of episodes + menus/extras could be bigger than 2x DVD5.
Or find a software that does rip to mkv/mp4 with subtitles.
Which software are you using to decrypt? I vaguely remember AnyDVD dis-recommending ISO rip mode.