Are you sure that she is my sister. I am really confused with all this stuffs. Let me make it more clear about our relationship tree.
Me < My mom< Mom's Father (Grand Father)< Mom's father father (Great Grand father)<His brother< Daughter< son< Daughter
In fact about this relationship, we came to know the previous month. I haven't met her father ( My Gf's father yet). So just help me to undestand this complicated stuffs.
I did some research,but it is way more complicated to understand for the one who doesn't know much about our Indian Culture.
Please , help me to understand this, Can I marry her or not??