I don't know if you can help me but i have found 3 skeletons but i didn't receive the achievements. Do they need to be completely uncovered they keep having a coffin on top of them for me, what do i do?

Yes they need to be completely uncovered. If you get a coffin you just have to wait until they show up again

Thank you so much!

You're welcome + good luck finding those skellies c: