This is a great question. My answer will be less reliable than what nature tells you when you do the experiment.
Here's my guess. The force between the two nozzles will be approximately equal to the sum of the forces that each would produce if it were the only one with flow. A nozzle that is sucking in water will pull the oher toward it. I think that two nozzles each sucking water in will be more strongly attracted, not repelling. If instead one is an outlet and the other is an inlet, I think the total force will be small.
In addition, ther are Bernoulli forces, just to make life a bit more complicated.
But I'd love to hear the real results.
Mike W.
(published on 05/09/2019)