If the family had left in early spring (April/May) its possible the father could build the house/barn (say a month) and still have time to put in the crop (late May/early June). As for the pregnant mother, you are looking at it from a modern perspective; in the 17th century women would be working until the baby was ready to drop and would be back at work within a week, if not days.
Looking at the background...
So in the early spring, the father chopped the wood and made wooden boards out of the wood... and put the ban up... I don't think so.
If we were talking about log cabins, maybe. But the house construction were too complicated without the help of additional people and a mill. (review the trailer and look at the buildings)
Good point, but to much time spent on the witches would have spoiled the movie which is more of a psychological horror story, then a traditional horror movie with a "monster."
I was reading that the goat seemed to play a key parts in the script but they couldn't make the goat act therefore the story was altered. I do think the goat needed more spotlight in the story.