Bananaa,
First off your trip sounds like a good time no matter what. Keep your purse/wallet with you at all times, don't let no jokers take ir from you and you should come out ahead no matter what you do.
Since you'll be in the area for a good two weeks, I highly suggest the side trips off the "beaten path." Also especially since you're both capable with the language.
Between the two cities, I enjoyed Barcelona a bit more than Madrid. Avg temps in the Barcelona area only get into the low 80s though it can be humid. Madrid can be warmer (low 90s), but it's inland so it's more dry.
In Barcelona check out Guell Park and
La Sagrada Familia. The latter is just a behemoth. You could spend all day there. I believe this site has a recommended
itinerary for Barcelona that I don't have any qualms with. I also recommed a side trip to Seville.
The only thing that worries me about your trip is it's in the middle of the summer, which is peak time for tourism, so be prepared to be patient at certain touristy spots and maybe plan on more than a "day or two" in a small nearby village.