What is the ruling on the in-laws deceiving their son's wife by concealing his illness from her, and what are the implications of their action?

We advise you to supplicate frequently for your husband and to perform Ruqyah Shariah (Islamic exorcism/healing). If your husband and his family concealed his illness from you, they have wronged you and deceived you, and they are sinful for that; because concealing physical defects is a forbidden deception. You have the right to seek divorce if you are harmed by remaining with him; because evident harm is one of the justifications for seeking divorce. His family must support him and assist you.