Is it obligatory to inform one's brother about his fiancée's OCD, taking into account the repercussions of that on the family?

Advising one's Muslim brother is an obligation, but in this matter, there is an opposing factor: the possibility that the advice could cause harm to the questioner and her family if the engagement is broken. Averting harm takes precedence over fulfilling the obligation of advice, especially since the suitor might be content with the woman in her current state.