How to make collapsible iron grills run smoothly besides greasing ?

Far, What is your question ? I don't understand what your saying ? Or what your asking. Please explain.

Spray WD-40 in the joints where they attach and fold.

Hi,

Try WD-40 or soap bar...........good luck!

WD40-and oil or grease doesn’t work for long because of the salty breeze

Can you take them apart? Maybe there's some rust that needs to be removed.

Ah - salty air! Iron will corrode easier in salty air - If you can take them apart do so. Clean the joints well then paint with a rust proof paint like Rustoleium. You will have to continue to lubricate (with the heaviest grease you can to find) to protect the joints. This is the same issue the Navy has with old iron ships.