The first one is a member of the Euphorbia family and is toxic, however, this particular plant grows in Madagascar, so your radiated tortoise might be able to eat it.
The second one is gollum and is a member of the crassula family - edible.
I can't remember the name of the 3rd picture, but I think I'm remembering that it has milky sap. If you break one of the leaves does it bleed white sap? Then its probably toxic too, but also native to Madagascar.
The 4th picture looks like it might be a member of either the aloe family or agave. It would be edible.
Ok thanks, they are all found in madagascar. They went close to the Euphorbia however just left, but they nibbbled on the second one. I just checked, no milky sap for the other one