Fianc�e 15 yr old is skipping. ?

After many sessions with counselors and sit downs the child just does not want to go to school. We have tried taking him to the front door of school and he just leaves out the back. He will get up early just to leave the house and hide so that we can not find him. He stays hidden until we have to leave for work. My fianc�e has two kids himself and I have four. He has a 19yr old and the 15 yr old. I have two 15yr olds, 12 yr old and 9 yrs old. I am worried about going ahead with the wedding when we can't seem to control this type of behavior. We have caught his 15yr old and one of my 15yr olds skipping school although through school records my child hasn't missed any other day this year than that one. This does not mean that my child is the innocent one. They both tend to feed off of each other. His child opens up to me about a lot of things and I thought we had a great relationship. But, no matter how much I try to show him what will happen without an education he still will not go to school. I sit down and talk with him a lot but, it seems I can't do anything to deter him from doing this type of activities. The wedding is only a month and a half away and I am wondering if this is such a good idea. I love this man and we both know we have found our soul mates in each other. I am just worried the children that I bring into the marriage will start following the other children. His child is capable of doing well in school but, absolutely refuses to go. Anyone have any ideas? Should the marriage take place? What should we do about the skipping school? We have exhausted our options and hope that someone may have found themselves in the same type of situation.