I think he knew something was going to happen. One of Susan's friends was there during the day. JP made Susan , I think pancake and eggs, and it took him several hours to do that. ( probably had to mix the poison up in it) Gives Susan a blanket because she is cold. Behaving like the good husband. Susan felt ill so decided to lie down.
He takes the boys sledding. Then comes back to see if whatever he had put in her food worked. Has to clean a mess, possibly vomit. Then we are supposed to believe he went camping to make smores where he had less amenities than at home. Yeah right.
And one other thing it was reported Josh didn't allow Susan to use the computer. Why? Could it be because the rotten apple didn't fall far from the tree.
Definitely a team effort here.