Help! need help please!!!!!!??????

Try explaining to them that they may not like it and explain to them what you are going to be doing. After that, promise them that your family and your sister's family can get together with the two of them and do something fun after or before your trip. Try to get them excited and planning this event so that they forget about your trip! Promise to bring them back various things from your trip and also send them postcards. Don't worry as long as you nicely explain the situation to them everything should be okay. Good Luck!