My fiance has psoriasis and in the future we want to have kids. what is the likelihood that our kids will get/show it, and will they carry on the gene

Small risk: There is a genetic component to psoriasis so there is a 50% chance a child will inherit the predisposition. However, even if that happens, the risk of developing psoriasis is relatively small. One large study put the risk at about 12% if a parent has the disease but I am not sure that the exact risk has really been definitively determined.