Some of the worst bits in no particular order.
The Street has a Bistro at one end and a medical centre at the other. So naturally you take the woman who is bleeding to death to the restaurant for help.
The armed police taking Roy Cropper's word for it that the gunman was dead and putting his gun down. It's okay, he's dead. Cheers mate, I'm off home then, don't need me anymore.
Hostages, witnesses, and possible murderess allowed to stroll around the street and wander into various houses, people ducking under the police tape as they felt like it.
Teenage Faye allowed to stand by the police tape holding the newborn baby she could have killed while an armed siege takes place just feet from where she stands. Plus every other nosey bystander not invited to the wedding milling in the background.
Gunshot from the kitchen, no screams or cries of "Michelle!" from the restaurant, just total silence from all those people who are supposed to actually care about her.
You're trying to escape the police, you need a hostage, you don't want to be noticed. Your hostage options are limited but the woman in the wedding dress is probably the most conspicuous person in the room. Pick her.
And possibly the most unbelievable bit of all. The whole street is aware that Steve kissed Michelle on her wedding day and caused Robert to drive away. Why was Tracy not kicking off and threatening to kill the pair of them? It's impossible that she doesn't know or won't find out, and it's completely against character for her to not be on the warpath.