So I plan to delete my previous seasonal character and create a new one, would it reset Fughar's daily quest and other seasonal challenge quests?

Hi Cheffy!
Don't think it would reset fughar's daily quest since you will get knowledge when you finish the daily quest.

Knowledged earned from daily quests were shared across family. So, I don't think it will reset the knowledge. However, it was not mentioned anywhere if the seasonal rewards will be reset or remained as progressed from before deletion. But some said that the seasonal rewards/mission (icon on the top right corner) will remain as where it progressed and will not be resetted since the rewards are family bound.