Hill Crest - it is something on the top of a hill (not just a hill), so I guess it should be - Верхнее or Пик
Crown Island (island) Короний Остров I'd say it doesnt sound "right" in Russian, can it be "остров Венец" for example?
United (coastal-Lake) Спольное Spol'noye - in Russia we won't recognise this word, maybe it works for Ukraine but not for us, we say "Сопредельное" or "Сопределье".
Peace (inland) Покой Pokoy may also mean a room in a palace - Мирное, Спокойное