Hello Evidence suggests that risk is higher in person who have family history but those who don’t have family history affected by it too [ as you mentioned that your fiancé’s mother ( she didn’t have any family history ) ] So there is no red line mark like thing that who will get that illness and who will not ( including you and me can get that illness too ) And there is no such term like mild borderline schizophrenia at present ( recent medical advances in form of tablet or injection can manage it nicely ) And most of the time schizophrenia can be well managed by timely diagnosis and treatment So you can continue your future plan with your fiancé Have a happy life

There is risk of genetic inheritance in psychiatric disorders but the risk is really low. Also the people who don't have any family history can get a psychiatric illness. Cannot say anything for sure. Also this is not a reason not to marry someone

Hello, Risk is slightly higher than that in general population ( 1% vs 8%). But really not a reason not to marry someone.