Problems with animation

I have to animate several characters. I have bought the assets from here: POLYGON Western - Low Poly 3D Art by Synty | 3D Historic | Unity Asset Store

But the problem is that multiple characters are in one .fbx file and if I import this file to mixamo the models are overlayed. I have tried to import this .fbx file to blender and deleted there all characters until I had only one left and saved the file as .blender but Mixamo can’t upload .blender files. So what can I do?

U can write to owner this asset bundle, or download blender ( for example ) and save each model to a separate file