How can I find my nephew and neice was told they never adopted they be 17 and 20 now

Definitely try to touch base with C & Y. If not adopted, they should have records, depending on the situation and time that's passed. Also, Google the name of the 20 year old. There is also something called Intellius (not sure of spelling). Don't know if it is free or not. My cousin searched and found my wife's biological brother through that. He entered the name, approximate age and last known location and had the address and phone number within ten minutes of me posting on Facebook for help. It also searches different spellings of the name, which is how he found it bc adoption records spelled her biological father's name slightly different from the way her brother spelled it. Now he was much older (67 at the time) so I don't know how that might affect a search but it's worth a shot. Good luck

If they were never adopted the names should be the same. The 17yo is a minor, but the 20yo should be more accessible.