My in-laws are travelling to the US for the first time from Mumbai-Abudhabi-Rome-Detroit. They are indian citizens and travelling on a tourist visa. I wanted to know about the security and immigration procedures at the airport, basically a guide on what to do and where to go. I have heard that we have to do US immigration at the Abu dhabi airport itself (would like to confirm this).

For Rome-fiumicino airport halt, I am assuming its just the regular procedures for transit unlike most of the other international halts. (please confirm this).