The characters who team up in this group are a cowardly magician hoping to make it on the frontier (Rick), his fiancée who wishes he'd act a bit braver (Diana) and a priest that tries to give Rick advice to deal with the whole situation (Yurald). In the final dungeon, with you controlling Rick, they take the fourth path and face a knight-like creature that shoots out glow balls and is only vulnerable when it disguises itself as Diana. The name comes from Yurald's powers, which are supposed to keep CIMA from attacking you...because I don't know exactly how they work.
Rick is a good natured young man, however he's not the epitome of bravery. In the dungeon you get him in, Rick not only has to be prodded to even go through the first two levels, but runs off when a CIMA appears which lands himself, Ivy, Philis and Yurald in a Teleport Trap. And in the next dungeon, Rick runs off crying when he gets too close to a CIMA after volunteering to hold a pressure plate down. Diana ends up breaking up with him in a fit of anger as a result, but in the dungeon where you find Jean, Rick proves his worth. He not only protects Diana when they're all alone, but also directs Ark and the others to step on a switch and cross the bridge, as well as stand on a dangerous switch himself. After that, Rick becomes a much braver person, and is able to win Diana back. Oh, and his power attack involves him spewing pink fire out of his wand...yes, pink fire.
For all her complaining, Diana truly does love Rick, she just wishes for him to show her what he's made of. After she breaks up with him, Philis deduces that herself, saying that if Rick thought he didn't need to impress her, he wasn't going to try to be brave. She flirts a bit with Vanrose and Ark, much to both of their dismay, but from her base comment right after that dungeon it seems she's doing it for Rick's reaction. And even some of her conversations during the break up mention her wish for Rick to be a real man. Once he truly proves himself to her, she calms down greatly, having more words of encouragement for him. Though she does give Rick the stinkeye about the monster that turned into her...telling him she'd never forgive him if he ever really hit her (Rick's comment afterwords suggests that Diana is still in charge in their relationship).
While Yurald is like Claude in that he has no connections to any other characters, his interactions with the bickering couple are enough to make up for it. Every time Rick isn't brave, or is fighting with Diana, it's usually Yurald who gives him advice; though since he's a priest, it tends to be more spiritual based, which is pretty much what Rick needed. According to the book, and deduced through an early Talk session in the Tutorial Dungeon, Yurald didn't originally believe in the Gate World.
Outside of the group, there aren't many interpersonal relationships. Practically the only one is the friendship between Rick, Diana, Vanrose and Shelley. Most of the interaction was within their group or confined to one or two little scenes. I guess you could count Rick seeming to hit it off with Ivy in Weakling Forest, or Diana's excessive flirting with Ark and Vanrose during her attempts to get Rick to shape up.
All ages taken from the Character Books in the Blue Creek from both CIMA: The Enemy and Frontier Stories. Starting Trust is the Trust held by the pioneers at Game Start/After Jester's Death.
*Though Rick and Diana's ages are listed as 28 and 26 in the game itself, their listed ages in the instruction manual are 24 and 21. I'm considering the game ages to be the correct ones here, but am making a note of the discrepancy. Diana's might have been a screw up between her English and Japanese ages, although the Japanese version wouldn't be produced for another two years.
In addition, looking over the Japanese manual, Diana's age is listed there as 20, while her Character Book age is 21. Going with the game over the manual here again, but man this group really didn't have much attention paid to them when organizing things.