Web Appointment letter & DS-156

[sampathgowri]

My Parents are going to attend the interview in Chennai.
1. Have they to take 2 web appointment letters(one for each). It was booked together for them.
2. I submitted DS-156 online, which generated barcode by itself.(I hope this is what is called as submitting online). I made mistakes while typing , so i resubmitted it again. As i submit it again and again, it generates new barcode. Is it ok. Have they to take the last generated one.?

[immihelp]

1. One appointment for both of them.
2. Take last one.