Talk to Endocrinologist on Cousin Marriage And Genetic Diseases

A protein c deficiency is running in my family.My elder sister marry to cousin and unfortunately her 3 children face neonatal purpura fulminans soon after birth and they could not survive and died within a month and one child(girl) alive only and healthy.Later on my sister face diabetes and heart problem and some psychological problems and severe depression and after all she develop deep vein thrombosis(DVT) and pulmonary embolis(PE) and she died in ICU.Now my family force me to marry my cousin.she is my double cousin.so my question is that,is this marriage is safe and healthy because protein c deficiency run in family???