I haven't seen The Hamiltons so I can't comment on its relationship to this movie. The story of The Thompsons isn't told linearly but it starts more or less in the middle and then backtracks. I'll summarize the story linearly.
An American family of vampires (one girl, 2 guys, 1 kid) try to mind their own business and are driving around the desert when the kid gets shot accidentally when a bunch of thugs hold up a diner. Now the family is seeking help. Someone tells them to go to Europe and also gives them a name. One of the guys, Francis, travels to the English country side to look for this person who can help them. The twins (guy and girl) end up in Paris having fun. While the other guy watches over the kid.
Francis drives around, his car breaks down but he makes it on foot to some family pub where he draws the attention of the locals. The daughter who works there is attracted to him. But it turns out the owner and their two sons are vampires. They take him to the main vampire who offers to help if Francis calls his entire family to meet him in England. They make the trip but things turn ugly. The main vampire and his family don't have the Thompsons best intentions in mind.
A lot of the movie is told in Francis' voice overs. The filmmakers know how to put the creepy small town English country side to good use. I really enjoyed most of the movie, but when things become physical near the end, the movie loses steam. The main problem is that Cory Knauf who plays Francis (and co-wrote the script) is just too laid back. Even when he's being attacked and his life is at stake, he never loses his cool. He does a good job with the voice overs, but acting in dramatic situations is entirely beyond him. A huge plus is the attractive girls, and there are many here- all of them actually. Elizabeth Henstridge is particularly lovely, attractive and hot. What a gorgeous girl. She basically steals the show. There's some nudity too. The special effects despite being CGI are pretty good and the fangs for once look convincing. There's a lot to like here, the creepiness, the English locations, the story overall, the women. There are some plot holes and details that make no sense. I look forward to the third one and will have to check out The Hamiltons. This movie is a good effort and a very good entry into the vampire genre which has been so mercilessly abused.
