I don't think Juventus will give Sevilla as much chance as Manchester United. Sevilla played a few good matches this year. However, even getting to this stage was a big surprise. While I thought they would be eliminated earlier, they managed to easily beat them on Manchester United's worst day and pass the round. Now it will be Juventus matchup. If they do not want to face a major defeat in Italy, they must prepare very hard.
Sevilla are strong enough to create chances by themselves and they don't need to have airdropped chances like from Manchester United players. Sevilla players are very confident about themselves in Europa League and Juventus will have to play with as highest carefulness as possible. They will not have easy match in Seville where Sevilla simply destroyed Manchester United in a second leg quarter final.
In the Roma-Bayer Leverkusen matchup, two equal teams will compete. Both teams can advance to the next round. I am sure they will work hard for it. Roma may be having a hard time in Serie A, but they will have a different concentration in the European league. With the experience of Mourinho, they also have the power to pass this match.
Leverkusen have less tired players than AS Roma and it can be a very big factor which can decide aggregated result between these clubs. Roma only have enough players for their squad and if one or two players get injured, can not play, they will struggle to have solution from their bench.
Leverkusen can find good replacements on bench and in two semi finals, I believe substitution players will be important for final result.