Danny told Amber when he set the weekend up with her that they were going to Waimanalo, which is just outside Honolulu to the northeast. And indeed it was Danny's car she was driving as we saw the license plate "DV2 399" whien she drove away from the camera, which has been on both of Danny's Camaros.
The door to the second house at least, most definitely opens outward because the exterminator had to step backward when the wife opened it. Perhaps they are designed differently in Hawaii for some reason of being in the tropics or something. But you could put a plank on both of those houses and prevent the door from opening, if you put the nails or screws into both the door frame and the door itself. What I don't get is how he put the screws or nails in the door without them hearing. They had to have been inside.
They really didn't say where Grace was, but I thought maybe she was staying longer in Jersey visiting her grandparents. (I'm assuming she went with Danny when he went to testify.)