Tinfoil Barbs are shoaling fish and need to be kept in groups of 6+.
They also get very large, 30cm+, and a 50gal tank is not enough, by far!
Silver Dollars - well pretty much exactly the same as I said above, very similar in max size.
Two adult Angelfish will only tend to be compatible in that space if they are a breeding pair. I'd only keep one Angel or 6+ in a massive tank so they have space for territories but I'm talking much bigger than 50gal again.
People forget Angels are aggressive Cichlids when they hit sexual maturity.
I'd go for a breeding pair of Angels and a nice big group of Corydoras and a shoal of Rummynose Tetra or something of a similar size.
I can elaborate if you'd like to know more.
EDIT; Dang, auto correct sucks..