The electrostatic force between two charged object is given by:

where
k is the Coulomb's constant
q1 and q2 are the charges of the two objects
r is the separation between the two objects
We see that the force is inversely proportional to the square of the distance:

. Therefore, if the distance is doubled, the force decreases by a factor 4, and the new force will be:

and it will still be a repulsive force, since the two balloons have charges of same sign.