Ski resort and trip planning Europe

We are planning for a ski trip and need advice on where to go, prices etc. We would be really grateful if some of you could help answering the following questions and give general advice on the topic:
1. Where are the best places to go for freestyle/freeskiing, that is ski parks in Europe (for skilled but not expert 15 year olds). We live in Norway and are thinking Germany or other countries not too far away to save travel time.
2. What is a typical budget for a long weekend or a one week trip in the winter holidays (end of February) for a family of four with two fifteen year olds?
3. Should we book through an agency? Do you know any agencies that offer ski trips including ski pass, flight and accommodations?

We have never tried this type of holiday, so we are not sure where to begin :)

- HH