Anytime someone has to remove a hose from anything it normally takes 2 wrenches 1 to hold the fitting and 1 to turn the nut on the hose.
the problem arises when there is limited space or surface to hole the fitting especially 90°
there are special socket like tools for this called weather-head sockets made by many tool companies the problem with them is you need to also use a ratchet with them and they are mostly designed to install the 90° fittings not tot hold while tightening the hose to them.
Yesterday I needed such a tool to remove a hose from a brass fitting on an oil cooler any twisting motion will result in a cooler tube being broken
I tried using a regular open end wench but there was little surface area to use it so I made a special hook over wrench to hold the fitting with
I call it my 10 minute 15/16" 90° fitting wrench. First I thought I would set up my mill to cut the hook portion of the wrench to fit the fitting but I didn't want to have to spend an hour or more setting up then milling with a customer standing around waiting.
quickest solution a few quick cuts with a torch a few minutes with an angle grinder just to knock off the rough and make the notch fit job done
This picture shows how well the wrench fits the fitting