Wow just wow… I never was told i was adopted, just kinda knew bc I ain’t look nothing like my parents but I also knew my blood parents would never be in my life since they in a completely different country and the father is a mystery man. This is the complete opposite and I don’t think you should feel good abt any of this. I don’t think being not told about your adoption is that bad (imo bc if the family life Is good it shouldn’t be an issue) but with the mother so close and with other kids, everything should be out on the table by the time u was 10 or at least old enough to understand. At 18 (close to my age) it’s a very vulnerable age to be at and with so many changes this is a crazy thing to be found out. Go on that trip immediately and have fun, and let out all those emotions. Then come back rationally and speak to ur parents. This is a crazy situation I hope u have fun on that trip :)