Let's not judge people by their reactions 6 or 7 months ago, when so very little was known to them about the investigation into Haleigh's disappearance. It may very well be that TN was crazy about MC and the kids were too. Remember, she was trying to get into the family. She was surely on her very best behavior. MC was happy, she had a place to live (she has been homeless), a man to take care of her and protect her from being in the streets, children, a almost MIL and Granny. She was eating, she had a roof over her head where at least her own family wasn't raping her. People were good to her and she was feeling the love and it was going pretty good for everyone. None of them would have ever expected this horror to occur. They would say very good things about her, they loved her and didn't for a minute think she was lying.
Then they started hearing things that made them not so sure. TN has been wanting to search the woods from early on. They are living it, and starting to wonder about MC. But, they don't want her to know it and they don't want it to be true. They have doubts.