Answer:
the distance should be changed by a factor of √2
Step-by-step explanation:
The attractive force between the couples can be given by Newton's Law of Gravitation:

where,
F = Attractive Force
G = Universal Gravitational Constant
m₁ = mass of the first person
m₂ = mass of the second person
r = distance between them
Now, if we want to halve the force without changing masses, hen:

Hence, it is clear that the distance should be changed by a factor of √2