How to best quick fix worn out tyre
There are several questions here.
You were on a road trip and found a hole in your tire...

I swapped front and rear tyre to have the weak one in front because it gets less pressure. Was this correct thing to do? Also, should I have deflated the air pressure in tube when I saw this?

And...

Should and could I have put both my old and his old tyre to prevent leak of the tube? It seemed like a good idea, especially because they were damaged at different places, but I didn't want to risk some other stupid thing that might have happened. If that would have been a good idea, what about if the tyres were damaged at the same spot? Would then make sense having both of them?

To summarize:
You found yourself in a bad situation and improvised several amazing solutions using what you had on hand to get a little further down the road until you had no choice but to walk.
Your solutions were the best you could do in the situation.
Suggestions:
Do an equipment check and solve problems before you start your road trip. Identifying marginal tires, brake pads, etc. and doing basic maintenance before you start on a trip will reduce (not eliminate) issues on the road.
What your bring in the way of spares and tools depends on how long your trip is.
You brought a spare tube and the tools to install and inflate it - which is excellent. On your next trip consider bringing a spare tire. As a rule of thumb its nice to have a spare tire if you are going to be riding further from home than you want to walk back. Even if your tire is new they can be damaged while riding in a way that requires replacement.