I also think those open windows will come up at trial unless there is a logical explanation for them such as it was a mild night or the victims were in the habit of opening windows to let out smoke/odors or sleeping with open windows.
I do think Jake could have fit through one of them, but I do not think the windows are how the W's gained entrance to the trailers. The open windows may have been an effort to stage the scene, but I honestly don't know if they mean anything at all.
Jake's appearance seems to have improved while he has been in jail. This could be due to him being relieved it is all over, no more running looking over your shoulder. No more waiting for the other shoe to drop. Now he knows exactly what he is up against.
It could also be due to no drugs in jail. If he had a drug habit that caused him to be thin and pasty then being in jail would improve his looks.
IMO it is the drugs angle. I have thought many times he looked like he might be taking meth or some other drug. If so then that is why his appearance has improved in jail.
JMO