My mom married my dads best friend since childhood and had my sister but my dad also liked my mom and her likewise. then my grandma (dads mom) found out my dad was crushing on her and was distraught (my grandma had not too long before that talked shit about a similar situation with other people). She wanted to separate my parents so she sent my dad to study in the US (grad school). That didn’t work, my parents planned to get married, and then my dads mom accepted her fate and called my moms parents to get to know them more except my moms parents said they don’t accept my dad as their daughters husband and only accept my sisters dad. Then my parents moved to the US and they didn’t tell any of us kids about it (even my sister). They planned to introduce my sister to her biological dad when she turned 18 but in actuality we found out when she was 14 by snooping through citizenship forms and asking grandparents about it.