Wouldnt Devoe and Kelly be dead within a couple weeks due to radiation?

Well, they were "quicly" picked up by a radiation, medical team and was probably scrubed naked and showered down for hours. Then was given pills for radiation sickness.

Their hair would have started falling, probably after they had beer. But they will survive.

No. Weapons grade plutonium is safe to handle. You can literately pick it up with your bare hands and be fine. Long term exposure wouldn't be a good idea if you were to handle is every day, but the amount of radiation you would receive is less than getting an x-ray. It needs to be compressed to critical mass by the explosives.