Now you only have 1 title and that one will be inherited by your heir. If you have more than one son, those titles would've been split. This decision will destroy all the titles that you own and only give you one in return. Unite the Spanish thrones when Alfonso is very old. Rinse and repeat until you kick the Muslims out of the Iberian peninsula. If the abduction scheme was not successful and you have to fight an similar or superior army, just call your French allies. If successful, you will be at war with the guy you just abducted, thus having 100% warscore. Then, a few days before the scheme fires, declare war on your target. Bribe agents if you need to raise your success chance.

As you said, the southern Emirates are quite powerful and are allied to each other.

Once you advance in your piety level, you can declare holy wars for duchies by spending piety. That will grant you piety and will advance your piety level, or get you close. You can do something similar with Aragon, or you can let them live. After you're done with your brothers, try to break the alliances that Navarre has by killing one of the people that make those alliances possible. Once you kill the king of Castille, offer one of your cousins to the legendary 'el Cid', thus bringing him to your court. You should go for the trait kidnapper and all the traits that increase you hostile scheme success chance. Also invest in the first tree in the intrigue lifestyle. Put your sister and lover in the position of spymaster and start murdering your brothers.

You have to marry one of the girls that have claims on Aragon. You can easily deal with that once you deal with your brothers. This way the King of Navarre can get an weaker alliance with France. When you start the game, invite your sister to court and make her marry the king of France.

Crusader kings 2 spain