My family is Vietnamese and we make Pho often. For anyone who isn't familiar its a beef broth soup made my stewing beef bones and knuckles. At the end of the pot there's always a bunch of beef bones at the bottom and I was just wondering if it would be safe if I cleaned these out/reboiled them and gave them to Elf to chew on. The bones are stewed with other random spices along with onions which I know is no bueno for doggies though.

Cooked bones are a no no. They'll splinter. Keep em raw, and avoid weight bearing bones, such as knuckles.

ooo ok we always have raw bones in the freezer, any idea on how to keep them from getting all rotten and icky? or should I just take it away after a little while and refreeze them/

I've fed soup bones and knuckle bones raw, but would never feed them cooked. I wouldn't imagine the spices would be settling for their belly either.

My dogs always finish a bone in one round. I've never had to refreeze anything with the exception of a 3 foot marrow bone, haha. But you can wrap them up and refreeze them.
I feed weight bearing bones but you have to really keep an eye on them as if they're going to town too roughly on them, a chipped tooth is not an unlikely occurrence. My boy did get a very minor chip from a soup bone before.