Actually, the way you've asked it, just sum the forces--that's easier than switching to an energy-based formalism.

If you have vector forces f1, ..., fN, then the "blend" is, literally, f1 + f2 + ... + fN. For instance, if you're an electron at the origin, and there are protons at positions (x1,y1,z1) , (x2,y2,z2), ..., (xN,yN,zN) then the force on you is k0*e^2/(x1^2 + y1^2 + z1^2)^(3/2)*(x1,y1,z1) + k0*e^2/(x2^2 + y2^2 + z2^2)^(3/2)*(x2,y2,z2) + ... + k0*e^2/(xN^2 + yN^2 + zN^2)^(3/2)*(xN,yN,zN), where e is the unit charge and k0 is the Coulomb constant.

Gravity doesn't magically appear anywhere here. Electrostatic forces blend to give...an electrostatic force (in a fixed reference frame).