So, I think I see a few things here.
1. First, I hope you mean have her in marriage.
2. "They dont think she is in god's will." Read 1 Tim 2:1-7. What do you see there? Read also Psalm 139 - God made and calls all.
3. I pray that your family be in concord and that you may enter into discernment with regard to this woman.
4. The good thing is you don't have to be strong, in addition to Scripture, we also have the Church! Have you considered talking to a priest about your situation?