Holst (Hilda's brother, not a parent but I think this should extend to relatives in general): Tall, bulky. Dusty maroon hair, wild and messy, maybe some stubble. Pink eyes. Probably a grappler class, but I'm picturing him in more formal looking outfits. A simple suit normally, he was wearing one when drinking with Nader, man I wish we saw that scene...his shirt came off at some point during that though after Nader's did. Vases and plates broke. Burping and farting happened.
Claude's Mom (Regina): Average sized (yet strong and bulky) woman with green eyes and long black hair. She's got an air of authority about her and is definitely a striking beauty. I can see her wearing something similar to what Judith wears. The other nobles of the Alliance tend to think she's a rebel for running off with "that Almyran", they talk crap about her for that. A lot of them secretly think "good for her, you go girl" but don't say it.
Claude's Dad (Emil): Kind of tall and skinny, blue eyes and short dark brown hair. Tanned skin. Kind of a bratty personality, a "I get what I want" kind of deal, which was what led him to attempt courting House Reigan's next in line. People were surprised he actually succeeded. His main goal was actually to help relations between Almyra and the Alliance but of course the pretty thing next to him wasn't just desired for that. The Almyran king is his older brother, so he's technically next in line unless his brother fathers an heir any time soon.
If nobody else designs Count Gloucester I might take a crack at him. @Anacybele, come design Sylvain's parents!