Increasing the two objects will cause the gravitational force between the objects to decrease.

"Increasing the two objects" doesn't really mean anything. 

You could increase the height, weight, cost, temperature,
albedo, and price of the two objects, and none of it would
have any effect on the gravitational forces between them.

You'd have to change one or both of their masses to have
any effect on that.  Then if you increased the product of
the two masses, the gravitational forces between them
would increase.