I'm wondering if you have the pump head set straight. It's possible - actually kind of easy - to get the pump head just slightly crosswise on a Presta (a not o) valve, so what happens when you press the plunger is that pressure just builds up inside the hose but doesn't go into the tube because the valve stem isn't depressed.

Without having watched all the videos and I'm not sure what's already been explained here - a Presta valve has no spring. The valve is held closed simply by the air pressure inside the tube, and the lock nut on the valve stem is just for extra security when going over bumps. So the corollary to that is that it needs air pressure from the outside to open the valve and fill the tube. But if the valve stem is jammed up against the gasket, which can happen if it isn't exactly straight, then the valve will never open. That's why it can be so very hard to pump a completely empty tube - without any air in the tube, the valve stem just wobbles around and is very hard to keep aligned.

I personally find it easiest to get the pump head on and straight at 12:00. Some do better at 6:00 - to me, I get too much pull from the hose in that position and I have to be bending down too far to steady the head effectively, but it's all what works for you. You'll want to hold the pump head straight - heel of your hand on the tire, fingers on the pump head - while you use your other hand on the plunger until you can feel air going into the tube.

Difficulty in getting the pump head on exactly straight can be a sign of wear in the gasket, too. Again, I didn't watch your videos - it sounds like your pump head has separate attachments for Schraeder and Presta? Most pumps use a single head, and in that case if it's been used much on Schraeder valves, it can wear pretty quickly to the point where it's no use on Presta valves. But even if it's only ever been used on Presta valves, it will wear. Every couple of years is a typical replacement interval. Rebuild kits are cheap and your LBS should have them.

As far as tire pressure - recommendations based on road conditions and rider weight are for the road. On the trainer, I would definitely inflate the tires to max recommended pressure to minimize tread wear and heat buildup.