Both strikers scored against Gillingham at the weekend, and Peter says:
"Marlon didn't score 22 or 23 goals last season by luck - he has got to keep being in there and working as hard even if things are not going well for him.
"In his last few performances he has been doing very well and he has to continue that and get even better.
"Teddy and Sergei can play up front and you have to make it as difficult as possible for them to get back in.
"If Marlon is setting up as many chances for Bobby or Teddy or Sergei we will be delighted.
"There is no doubt Bobby has ability and we believe that probably more than he does sometimes; he has to have that belief and the biggest thing for me is that he had a chance which the keeper saved and he has come back two minutes later and got the goal - and that shows character.
"People talk about the goals he set up and the goal he scored but coming back after the save showed more character than anything else.
"People always say strikers are judged on the goals they score but I always believe they can be judged on what you create for your team mates if you are not scoring.
"You can't just blame strikers if goals are not going in - if they are not getting the service they can't score.
"Hopefully Saturday was the start of something good for him and that he stays clear of injuries because they have set him back."
Speaking ahead of the Chelsea game, Peter adds:
"It is a break from the league and these are the sort of teams you want to play against week in, week out, and it will be important to see how far we have come - hopefully it will be a good experience.
"Obviously we are leaving it to the last moment to name the side because of the knocks we have and some boys being cup-tied.
"Playing against the best players always brings the best out in you - you respond to that.
"We are up against a team with huge financial clout but it is still important you make the right choices of players and there is no doubt they have done that, bringing in some world class players.
"But we are not going there as lambs to the slaughter, we are saying that there are boys with experience that have played there before on big occasions.
"We are going there to give a good account of ourselves and hopefully we cam cause an upset, that's for sure.
"West Ham United are a big club so there is expectation on us anyway; playing for this club you have to have enthusiasm every day whether you are playing Chelsea or Rotherham.
"We have trained and prepared the same way we do every week but we know it is a massive occasion, not just because of Chelsea's finances but because of the way they are playing.
"Everybody is a little bit fearful of them, but it is something as a player you have to grab with both hands because these occasions don't come along very often."
Peter is not entering the debate about what sort of side Chelsea will field - though Jose Mourinho has stressed his commitment to winning the competition - and says:
"It doesn't matter what team they put out; we know the system they play and the way the manager thinks; he is very professional in everything he does and wants to win everything he is involved in - no different from ourselves.
"Whatever side they put out will be full of international players, top class ones.
"But we have good players as well and hopefully it is going to turn out into a very good game.
"You have to earn respect in the way you play and we will not be sitting back as people may think - we will be having a right go and we will be disappointed if we don't play well or get the right result.
"It is eleven v eleven and yes, they have fantastic technical players, but sometimes you can match that with everything else you have got and if we play well on the night there is no doubt we can get a result."