> Where and how exactly is the radiation release of coal plants happening?
Coal plants don't burn pure elemental carbon, the black stuff that is dug up from the ground contains a lot of other stuff as well, such as sulphur (acid rain, etc.), and, yes, various radionuclides. So when the coal is burned, part of the radionuclides go up the smokestack, others are left in the ash.
Realistically, compared to all the other environmental destruction associated with coal power, the radioactivity release is a non-issue. At the same time, it's good to keep in mind that except for major disasters like Chernobyl, an operating coal plant releases orders of magnitude more radioactivity to the environment than an operating nuclear plant.
> I definitely don’t wanna promote coal, but where are these numbers proving coal killed and harmed more people than Fukushima and Tchernobyl and the many smaller incidents?
You cannot usually say that person X died due to coal power production (except for things like coal mining accidents (which are quite common), maintenance worker falling etc.), but at a population level coal pollution causes an increase in respiratory illnesses, strokes, etc. which, again, at population level kills people. If you want to learn more, you can start e.g. at https://en.wikipedia.org/wiki/Energy_accidents
> Also i often wonder - where could science of reusable energy and reduced consumption be if the billions invested in nuclear research were invested there instead?
I'm not sure what "reusable energy" is supposed to mean, but yeah, sure, energy efficiency would probably be better than it is now. Would it be better enough to cover the loss of nuclear energy, and it's partial replacement by fossil power such as coal? I doubt it.