Both MakeHuman and MPFB are open source projects with a split license, with the goal that there should be as close to no restrictions whatsoever on the graphics parts.
The asset license
All core assets are shared under Creative Commons, CC0. The effective consequence of this is that you are free to do as you see fit with the asset or derivates of the assets. You do not need to pay anything, include any copyright notices nor give attribution.
The source code license
The source code of MPFB is shared under GPL and the source code of MakeHuman is shared under AGPL. The full license texts can be found here for MPFB and here for MakeHuman.