here's what happened at my nikkah- the Imam came to the room with my dad, and my two witnesses (uncles).. he explained to me the hadiths, etc related to Nikkah and asked the witnesses to ask me if I was whole heartedly getting married and not under any pressure. then he himself asked me three times and I said yes. right after, we all gathered in one room with my husband's family and mine, and that's where he asked my dad to read durood shareef and kalma and asked about accepting the marriage on my behalf (i was sitting next to him). then he turned to hubby and did the same again.
i have seen nikkahs happening differently though, ours was a bit changed because the Imam wanted both me and hubby present in one room.. he said in islam, it's a woman's right because women can be easily oppressed so she should be present when her father and husband-to-be are saying qubool hai.. while in our family, the girl doesn't see the guy until after. so we decided to do the 'witnessing' ceremony (asking for my consent) seperate and then together, where only dad and hubby spoke.
thats how its in our families too.