They are threaded compression fittings. There is a flatish face on one side of the connection, and a matching one on the other half. There is about 1/8"width of contact face. maybe a 37* flare? The thread engaged depth is about 1/2". The fitting metal is kwikoxidizium white metal and quite soft. The threads corrode, the sealing face has a lot of friction, Murphy rules, the big hex for the flare/line nut wrench is a 19mm and the small one is a 14mm, the working angle is obscene for application of leverage, the 14mm hex is made of even softer stuff than the 19mm, perhaps lightweight kwikoxidizium.

It is somewhat possible to get the bleeping connector on the front end of the rubber loose. At least a better chance than the tank end. Some better, anyway.

Resist the urge to use heat to break it loose. You will not like the result.

In the event you can't get the front connector off, cut the hose and remove the tank plate and pump, then clamp the 14mm tank fitting in a vise, soak the thing in voodoo juice inside (thru the cut hose) and out. PB Blaster, Knok R Loose, Mouse Milk, or dexron and diesel plus acetone are all good penetrants. Cut off all the hose you can with a knife, and using a 6pt deep well 19mm socket, put the large fitting half under heavy tension, short of wiping off the flats. Strike the side of the socket sharp hard blows with a steel hammer to shock loose the joint. If you have an air hammer, it and blunt tip bit do a just fine and dandy job of shocking the joint.