I'm not sure about the Visa for an aupair, but I will say that I've been to spain twice on student visas and its a pain to get, and thats with being registered as a student at a spanish university, and I believe it took be about 2 months, both times, to get it from the embassy in chicago. im not sure going to england for the weekend would do it though, because i believe that you only have 90 days in a certain time period, so youd have to go to england for a lot longer than just a weekend... but im not sure on that so check.
As far as your 2nd question, tutoring or offering private english is often possible and a great way to earn some extra cash (at least in my experiences in granada, university of granada area). It wasnt students i ended up working with though, a family contacted me and i went to their apartment 3 times a week to play with the kids in English, very basic stuff since the kids were little, but it was a great deal!