If I'm correct that it's a camera orientation issue, then if AssetForge 2 supports generating thumbnails from the other side, that'd be the quickest solution. Otherwise, you can always rotate the models 180 in Blender, or use some mass model manipulation tool that'll do it more quickly.
This kit is in standard wavefront obj and the scale is correct for Unity units which AssetForge 1 and 2 use. There is nothing wrong with the models. There is a forum on the itch page for AssetForge. I think there's a page specifically for this model kit on there. I recommend asking your question in that forum.