Hi welcome to the forum
As said above Severums are quite flexible in terms of tank mates as long as the other fish are not too nippy or overly aggressive like big Central American cichlids or too small to be eaten theres usually a good balance to work out.
Firstly though I have to say that 3 Severums will outgrow a 60 gallon tank quite quickly. Do you have plans to upgrade the tank in the near future? Golden Sevs can end up the size of dinner plates - 12 inches long and tall and they get to a decent chunky thickness as well. Equally your plec will eventually reach around a foot long. To keep these fish long term, and the Severums and Plec can live for over 10 years you will ideally want a tank in the region of at least 180 gallons which is a 6x2x2 foot tank. Is something like that an option?
Then looking at your other fish, I would add more Cory Catfish. The great thing about the Albino is that you can mix them with the Bronze and they will still school together as they are the same species, as a shoaling fish they will do much better in a big group if you got the school up to about 10 it would be really good.
Malawi Peacocks are not a good idea with the other fish you have, they are best kept in a dedicated tank not a community tank like this. They can be very aggressive and they have completely different water requirements to the other fish, the Severums and Corys will want a ph below neutral and soft water where as the africans will want a ph well above neutral and hard water.
Lastly, what is your tap water like? What is the ph and do you know if it is hard or soft? This info will help us recommend other fish for you. But I would not add any other fish to this tank unless you can upgrade soon. Otherwise realistically you will need to rehome the sevs and the plec and look at a smaller species of cichlid.
Hope that helps - sorry its a bit negative.
Wills