As far as they know, they’re only a week or two in. Even their grandparents could still be alive in that time frame.

I never thought she was dead. There are many other ways the episode could have gone. But with that title, we already know what's going to happen. It was a terrible headline for a site like this.

If I remember correctly, he can change the past and come back to the present without anything being different except what he changed in the past. But, if he goes back to the past after his most recent return from the past, everything he did to change the past the previous time he was there will be erased.