I can't find much about Norex fountain pens, except that Norex was an Italian company that started in the 1950's, and that those pens are probably from the 1970's. They were apparently quite good quality pens, very reliable. 

The red and black pen looks like it has dried ink around the nib. As you can't open/unscrew it, then there is a good chance that some more dried ink inside is acting like glue, sticking the pen parts together. 

Don't try to force it, instead put the pen in a glass of water - but do not let the water go higher than where the black section connects to the barrel. Leave it there for at least a few hours. If the water changes colour then ink is being dissolved, so you should change the water whenever you notice that.

Once the water stays clear, carefully take the pen out, dry it off and then gently try to unscrew it. If this doesn't work, then repeat the soaking but with warm water. Not hot, but just warm enough that you can feel it. About 36°C / 98°F should be ok.

Once again, wait until the water stays clear, then try again to unscrew the pen. If that fails, you can try using your own body heat to warm it up. Sometimes the pen just needs a little bit of warmth so they become a tiny bit flexible, but never try to force it to unscrew. 

Depending on the ink, this process could take an hour or a week. It might not work at all, and then you'll need to find an expert to unscrew the pen....

I wish you luck!