The best tool for paint stripping in my book is... brake fluid. The one used in cars. You can buy it at any gas station and at many run-of-the-mill supermarkets. It is designed not to damage metal car parts or plastic pipes but also to prevent corrosion and remove impurities.
Start by pouring the fluid into a jar. Then put the miniatures inside:
Keep the miniatures in the jar until the paint starts to peel of by itself. Depending on the model shapes and paints used it may take a couple of hours or days. In this case it was enough to soak the miniatures overnight:
Pull the models off the jar using tweezers. Scrape the remaining paint with an old toothbrush. Note that any glue used on the models is very likely to come off as well. Be prepared for some glued parts to fall off.
Enjoy the models as new!