On one of the news show this morning, a neighbor took a reporter on a tour of her house - which is a replica of the crime scene. Didn’t look too big to me - and the camera tends to enlarge space. Also, it’s what I would call a “railroad” design - no hallways, just one room leading into the next. They didn’t show the upstairs but the kitchen led directly to the cellar.
Another possible alibi is provided per post #28. The brothers were described as useless drunkards. So, they could have been at the house and been drunk and passed out, and then kicked out in the morning.