I wanted to test the Aragon's situations so I played 10 turns. No cheating, no any special tricks, no reloading. I made some screenshots:
1. Begining - attack before Moors grow in strength.
2. Result - two cities conquered:
It was nothing extremely difficult..
3 Portugal asks for an alliance:
3. After that Moors attacked, I have maybe 4,5 battles. They have little heavy cavalry and I was using the hills to neutralize charges:
4 After these battles my super general :
5. At some point I had enough money to ask Spain for alliance, even though I released almost all captives:
6. Economy is not so bad:
7. Many won battles and alliance with two christian factions gave me very good standing with the Pope, crusade would be an effect of it:
In the end I could give Murcia to Spain for alliance, but I didn't have to. Also Moors asked me to become their vassal in the turn 4 and I disregarded that. Nothing that I did was super difficult. The battles I won because of using the mountains, the very good javelins Aragon has and using light cavalry (Alforrats) to surround the enemy and charge from the back + Garcia very good general. My reputation is only reliable, so potentially I may be backstabbed by Spain, but I just sign an alliance so I have about 20 turns of peace from them. From the north I have Toulouse that has a very strong rebel garrison and will not be conquered very quickly. I am just saying that its possible to win these game on VH and probably many people will be able to do it.