is there some kind of siectracide that will remover stumps?

i recommend you ask to a professional, to be sure that the product or treatment it is the ideal

You can drill some large holes and add salt inside the sump, it will cause it to rot out. You will need to reapply it. I think there are also products to rot them out. It takes a while to do it that way, if you want them out immediately best get a backhoe clip the big surface roots with the bucket and knock the stump over or dig it out if it is a tree with a long tap root.