Genetic Disorder

Patient: Hi myself Karthik VTBelow is my questionI like one girl who is very close friend to my home.she is having genetic problem in her family.Her Grandmother and Grandfather were very closely related.Got married and had 3 children. One son and two daughters.Elder guy was fine till he reached the age of 50 then he started facing the problem ( not able to bend the legs and hands, problem in walking )Elder girl is having 2 daughter. first one is married and have one son of 6 months agesecond girl i wanted to marry.But her mother also is facing the same problem as his brother now.the girl whom i wanted to marry shares the same blood group as that of her motherin her childhood, she was given with her blood as well due to lack of bloodWill she also in future gets affected with this gentic disorder problem?Will this affect our kids in future?please reply answer to this mail id .I will be waiting for the reply