At a minimum:
To make a practical bomb additional materials and systems would be required.
Considering the fact that any competent Physics Grad student using publicly available data could design a workable fission bomb (getting the materials to build it is another issue) having a yield comparable to the ones detonated in WW2; it is impossible to ban nuclear weapons. If a country wanted them it will take them roughly 4 years to build the nuclear materials processing infrastructure to make the needed materials.
Private individuals. This is not due to "legal prohibition" but to practical inability to obtain the materials, which requires the efforts of many many people working to this purpose. Any country that actually wants them can and will have them, it only take 3 to 5 years to build the infrastructure needed to make the materials required for them once the decision is made to acquire nuclear weapons.
NO! Nuclear weapons don't make and detonate themselves
They are taken to a plant that manufactures nuclear weapons (in the U.S. the Pantex Plant near Amarillo, Texas) where they are carefully dismantled and those parts whose materials can be reused to make new nuclear weapons are recycled. The chemical explosives are usually burned to safely dispose of them.
Do the Russians have nuclear weapons?
There is no specific name for people who create nuclear weapons.
No.
make sure nuclear weapons did not proliferate to nations w/o nuclear weapons
The new country that want to make nuclear weapons. And how to consult with they own weapons
NO.
The US no longer makes nuclear weapons, it only refurbishes existing ones that are wearing out.
materials