Yes, you can. Follow the instructions on the makehuman website.
I do not know what you want.
After import it will be a blender object that you can use as every other blender object.
Blender is GPL. You can sell Blender but you have to follow the GPL. Typically you do not want to do that.
Content created with the help of Blender belongs to you. Your copyright, your licence.
Blender licence with FAQ.
But be aware content imported from somewhere else does not turn to your property. Make sure to carefully read the licence of that content before you even think of downloading or using it. Some content does not allow usage, distribution or manipulation, or at least under certain conditions only.
Be aware the Blender Licence belongs to BGE games too. In difference to .blend files, animations or images you will distributes parts of Blender (the BGE) with your content. This means you need to be careful how you distribute your game.
Content bundled with the Blenderplayer have to be distributed under GPL. Content that is not bundled (=separate files) can be distributed under the licence of your choice.