Very doubtful.AFAIK, the minimum mass of plutonium/enriched uranium for fission to occur is at least 5kg; add to this conventional explosives and the containment, a hand grenade would weigh far too much to be practical.
Smallest nukes I know of would be 155mm artillery shells, which have been abandoned as too expensive.
Yes, and freeforall has not been heard from since 2010.