USA-B2 tourist visa DS-160 spouse details mismatch

[user138902]

I am filing DS-160 for my mother. I appreciate insights on how below situation can be handled.

1. Her passport has my dad's name without surname (ABC). But the name in my dad's passport is ABC XXX. I was thinking to fill the DS-160 as per her passport leaving the surname blank but it seems to be mandatory field. Should I fill FNU as given name and ABC as surname for spouse? (or) Should I fill my dad's actual surname?
2. Also, my dad's first name has spelling mistake (has one letter additionally) in my mom's passport. Will having an affidavit (signed by attorney) confirming different variations of my father's name as same be helpful in this scenario to avoid any visa rejections during interview?