What is the ruling on a husband saying that jinn know the envied person simply by looking into their eyes, and is this statement considered disbelief (kufr) that necessitates uttering the Two Testimonies of Faith, or is it a sin, or is there nothing wrong with it?

Your husband is mistaken for saying something that is not based on evidence, but he does not become an unbeliever (kafir) by doing so, because he is not claiming knowledge of the unseen. As for the soothsayer, he claims knowledge of the unseen and denies the texts that specify knowledge of the unseen for Allah alone, such as His saying: "And with Him are the keys of the unseen; none knows them except Him" and "Knower of the unseen, and He does not disclose His [knowledge of the] unseen to anyone Except whom He has approved of messengers" and "Say, 'None in the heavens and earth knows the unseen except Allah.'" We advise against the whispers of declaring someone an unbeliever (takfir) because they lead to great evil.