Perhaps 3-6. Each.
The two countries really only need two. Each.
If each has one, the two are in a propaganda war = Unstable.
If each has two, then the region is stable. Neither can attack the other first and be absolutely positively sure it will not be attacked in return.
But nothing - ever! - has suggested either country has made more than 5 weapons. Except this story.
The Tunguska Event in 1908 was the equivalent of 1000 simultaneous Hiroshima explosions and had a negligible effect on world climate.
The Krakatoa event in 1883 was estimated to have been the equivalent of 13,000 Hiroshima explosions. It lowered average global temperature by 1.2 degrees Celsius. Crop yields in the Northern Hemisphere were barely affected and in the Southern Hemisphere not at all.
What have these guys been smoking?