It keeps saying that I need dry grass and the villagers walk away to do something else when I set them on the grass.

You have to be at exactly the dry grass area where the message is "sees very dry grass".

I have the same problem. I have found the diamond in the fire now i want to relight the fire. I put my villagers to the dry grass, they see the dry grass but dont get them to the firepit.
What can i do now ?

Make sure you are dropping them on the right place. The dry grass is the really flat-looking spot below the fern, not the stuff between the waterfalls.

ok, ty, it was the false place, i drop them between the waterfalls

When you bring the villager near it, on the "action" bar it will be written!!

My problem is that my fire went out and I need to restart it to finish puzzles 12 and 13. I have the dry grass in the fire pit but when I drop my villagers onto the torches they don't pick them up. It says "Someone left some burned out torches here."
What do I do?????

you dont restart the fire with the torches. Just set an adult on the firepit and they will lite it.

Did you put wood in the fire pit too? You need wood and dry grass. After you have both of them in the pit, drag and adult onto the pit and they will light it.