party mechanics (skill checks and modifiers)

i like playing as party not just controlling 1 character, cuz honestly thats not how dnd is supposed to be played, one character cant be proficient in all skills, which is why the party is important, now in other dnd-like games, like pathfinder or bg3, the character with the highest skill (lets say stealth) rolls for the stealth checks + their modifiers if applicable

now what happened is that i sent my gloomstalker ranger to scout the room ahead while being as stealthy as possible. what franz does is to do a stealth check using my paladins stealth skill (which is nbegative), makes me roll for a dc of 14 without negative modifiers. which failed as expected. so i thought that was stupid of him so i gave him a second chance and called him out that the character he’s asking a stealth check is not doing a stealthy thing ergo franz should use the stealth check + modifiers on my ranger but what he does is he asks for a stealth check now including stealth skill and asi modifiers of the ranger but also increases the DC to 18, which she also fails but now because franz arbitrarily decided to also increase the DC.

seems like franz is deliberately creating a situation that makes my party fail no matter what, without good reason, and ive just wasted 5 credits trying to fix franz and all he does is apologize