I suspect Russia is worried about how well their nukes will work. The small tactical ones (battlefield nukes) are the most complex and so most at risk of a maintenance failure.
Russia's worst fear is deploying a nuke, only to have it fizzle. At this point it's strategic or nothing. Deploying a strategic nuke would cause massive political fallout. Far more than Russia could cope with. No-one, including China and India, want that genie back out of the bottle.