Hello Sophie!
First, you may want to consider allowing the goslings to learn how to fly to some degree in order to strengthen their flight muscles and insure that they know how to fly when needed!
I think it is truly important that if you are unsure of what you are doing, that you have an exotics/avian veterinarian perform the procedure for you to insure that the procedure is done correctly and to avoid clipping of too many feathers. Self-mutilation, sharp feather edges, blood feather hemorrhages, and falls are common in birds that receive inappropriate wing clips!
Once you are shown the proper technique, than you can easily repeat the procedure yourself with an assistant at home in the future!
If you feel comfortable clipping the wings, than I would use cat or dog nail trimmers to individually clip each primary flight feather. Do not cut into the secondary flight feathers, as your geese will need to have the ability to flutter at best if needed.
Here are a few articles to help you figure out how to clip your gosling's wings......please browse thru each article, as they have a variety of opinions and techniques which you may want to consider!
http://www.poultryconnection.com/quackers/clip-3.html
http://www.birdsnways.com/wisdom/ww19eii.htm
http://www.exoticpetvet.net/avian/clip.html
http://www.geocities.com/scribblyfaq/captivebirds.html
I hope that you found this information helpful. Please remember to PRESS ACCEPT so that I can be compensated for my time and professional recommendations concerning your pet. I encourage feedback and appreciate bonuses!! Best wishes to you and your pet,
Dr . Jodi Lynn Smith
Veterinarian
13 years of practice experience in exotics, small animal internal medicine and surgery.