After electrostatic balance, the charges on the three spheres are Q, -q and Q+q from inside to outside.

The potential of (1) sphere U 1 = q/(4π ε 0r)-q/(4π ε 0r1)+(q+q)/(4π ε 0r2),

The potential U2 of the spherical shell = (q+q)/(4ω 0r2),

Their potential difference u1-U2 = q/(4π ε 0r)-q/(4π ε 0r1).

(2) If the spherical shells are grounded, the potential difference between them will be affected;

Invariant, q/(4πω0r)-q/(4πω0r 1)

(3) If the ball and the shell are connected by wires, what is the potential difference?

Zero.