Yes definately crush the oyster shells. Try and get it to a very fine powder and than mix it with something they really like to eat. I have found that hardboiled egg works well. I chop it up and add the powder in, you can also add the powder to their water and they will get some that way.
That is really sad about the other babies. I am so sorry. Sounds very promising for him though, you will have to name him lucky or something of the sort I would look into adding oyster shell or another strengthener to your mamas feed, sounds strange that she was able to crush all the eggs...
I would recommend wraping a warm moist towel around him (not his beak) to soften the membrane and protect the vent until it is able to close up. Than leave the bator alone so the humidity can reach a good level. If he is breathing ok he should be fine for awhile If it has been 24 hrs and he is...