ご質問ありがとうございます。
① "I feel like he is still alive."＝「彼がまだ生きていると感じます。」
② "I can't help feeling that he is still alive."＝「彼がまだ生きていると感じてしまいます。」
③ "It feels as though he were still alive."＝「彼がまだ生きているような気がします。」
ご参考までに。
"彼がまだ生きている気がしてしまう"
- I can't help but think that he is still alive.
- I can't help but feel that he is still alive.
彼がまだ生きている気にしてしまう
- Makes me feel like he's still alive.
- It makes me feel like he is still alive.
アメリカ合衆国 
