I don't think we *know* what you said above.
One possibility is that Chad and Tammy no longer shared a bedroom.
From Mackey's testimony, we can infer that Garth did not worry when he could not find his father. At least, to me it sounds like Garth was frustrated because he needed his father for next steps, but it doesn't seem like Garth was thinking, "Someone killed my mother and kidnapped my father," or "Someone killed my mother and my father is off chasing them," or "My mother died and my father must be so distraught and in danger."
To me, it seems that Garth was not afraid for his father's safety that he couldn't find him. Just an inference. It seems like it just made it more stressful to cope with figuring out what to do.
I think it wasn't that unusual for Chad to be difficult to find.
A lot of communication occurred between Lori and Chad when Tammy would be right there, if Chad shared a bedroom.
Chad had location turned off his phone.
I think they had separate bedrooms. It might be that Chad went out sometimes after bedtime.
MOO