To be simple and clear I can say Barcelona is clearly not strong enough to play in the Champions League and they won't be able to beat the stronger team considering the situation in this tournament and we all know why, That's because Barcelona doesn't have superstar players and experienced players in this team and Flick had to use the young talents to have a cheaper team and avoid spending too much money and the bad financial situation of Barcelona is the main reason for it.
They have Robert Lewandoski who can have a good performance, but Barcelona has no other players to fill the place of Lewandoski in this team and there is the same situation for Lamal.
But the performance of FC Barcelona doesn't show that they can not perform well in the champions League this season following how they started this season, I understand that they lost in the champions League competition against AS Monaco but that look came as a result of the red card they received in the game. The team has no big names to Ike they used to have in the past but the coach has been trying to manage the players in his team right now and I believe they can end up getting better and better if they are able to manage the players in their best performance.
About the players you mentioned, the team is struggling to survive the financial crisis they are into finding a backup for Lamal and Lewandoski is not possible at the moment unless they will recruit young players from their youth team.