Character mistake: When Jonathan is closing the transactions in Dracula's castle, there is a close-up of Renfield's card, which says "R. N. Reinfeild." However, the end titles spell the character's name as "R. M. Renfield", like in the novel, and Dr. Seward also refers to the character by this name in the first scene where he is recording his diary on the phonograph cylinder, just like he does in the book. (00:16:30 - 00:23:20)
Character mistake: The telegram to Professor Van Helsing says "do not loose an hour" rather than "do not LOSE an hour." (00:55:25)
Character mistake: At the beginning of the scene where the vampire hunters leave London in pursuit of Dracula, Jonathan narrates, "By train we can reach the Romanian port in Varna in three days." However, Varna is a Bulgarian seaport. This can even be seen on the map showing the Turkish invasion of Eastern Europe in the movie's prologue, and on the map that Jonathan studies aboard the train at the beginning of the film. (01:45:35)
Answer: It's unlikely they were falling in love with Harker: they are sadistic, baby-eating monsters who regarded Harker as food and a temporary plaything. As for them sleeping in the open, the local populace dreads and avoids Dracula's castle, so there's hardly any fear of intruders. Van Helsing did enter and kill them, but they reckoned, mistakenly, that he too would be too afraid to do so, especially after their horse-mauling escapades the previous night.
Jukka Nurmi