I applied for both my parents' greencard by filing two separate DS260 forms. Both went for the interview at the consulate together and received a stamp on their passport. However, given my grandmother's health, my mother is planning to NOT come to u.s. within the prescribed time and as a result, won't be getting the greencard. However, my dad will come to u.s. - given he is coming alone and not with my mother, will he have any issues at the port of entry without my mom joining him? Anything that my mom should do given she won't use the immigration visa?