Hi, Brad.H. This probably isn't going to answer your question as you want to hear it, but it's the only way I can answer it in good conscience.
The first thing you need to do is determine the cause of your new additions' deaths. It may be a fish, but it's much more likely, considering your relatively peaceful stock, that it's a water quality issue. Please post your water test results so we can rule that out as a cause. It's something you'll want to make sure is on the up and up before adding new fish anyway. It would also be helpful to know how long the tank has been running, what kind of filtration you have, etc.
The second thing is to decide what fish to get rid of before deciding what fish to add. Your angel and your corydoras are appropriate for the tank. If the plecos are common plecos, they really aren't. You could go with a species that stays smaller, such as clown plecos, rubber plecos, bushynose, etc. The only thing I can find for silver sharks is Bala Sharks, which get much too big to be accommodated by a 130l aquarium.
My recommendation, once you test your water and determine it is appropriate, is as follows:
-return the plecos (assuming they are common) and silver sharks
-get four more bronze corydoras. They are schooling fish and will prefer the company of others of their kind.
-find another fish that you like that will stay smallish (rasboras, tetras, etc.) and post back what you found.
From there we can help you determine where to go with your tank and what kind of time frame you're looking at. The most important thing, however, is to get your water tested and post the results.
