I have all of them but one, the under wear under the twins' favorite and above the bandit's favorite, and as for the sniffet, it's the bottom row's right, please help I am out of ideas

Underwear #24 is Christmas Event, just temporary change your device date into Dec. 10~31 (last year) and check Liam in Tavern at night. Must also have max affinity with the twins.
Sniffet you are looking for is located at the King's statue at evening. Rulius might be blocking the path in the evening. You might need to go around General Grant's room.