Yep, Liverpool and Leverkusen must beat their opponents in the current round (quarter final) if they want to qualify to the next round (semi-final) and may have a chance to be in the final round. Atalanta and West Ham are 2 good teams, they often bring difficulty to big teams although they are not top teams. Even if Liverpool and Leverkusen could beat Atalanta and West Ham, they probably must fight with AC Milan or AS Roma in the semi-final round. It even can be more difficult than Atalanta or West Ham.
Currently, Bayern Leverkusen on difficult format drawing for qualifying to final of Europe League, although success defeating West Ham on quarter final Leverkusen will face the winner between AS Roma or Milan become most difficult opponent team.
Last season in Europe League, AS Roma success defeating Bayern Leverkusen on the semifinal round under Jose Mourinho era and I don't think easy for defeating the Serie A teams between Milan or Roma.
Seems easily for Liverpool drawing to final match, after facing Atatalanta on semifinal round then waiting the winner between Marseille or Benfica has easily than Bayern Leverkusen journey for qualifying to final. I doubt with ideal final Liverpool vs Bayern Leverkusen in Europe League this season.