Corydoras catfish do well with angelfish. This is a shoaling species so a group is needed, and here I would suggest 7 up to maybe 12.
Upper level fish are a bit more of an issue. You need to avoid linear fish as angelfish frequently see these as food. You need to avoid active fish as this annoys angelfish which are sedate. Any fish prone to fin nip must be avoided. In a larger tank, all this could be accommodated with a group of one of the disk-shaped tetras, such as Hyphessobrycon bentosi, H. rosaceous, etc. The problem here is the tank size. A pair of angelfish--and I assume this is a bonded male/female pair or perhaps two females, since both are still alive together after three years--in a 30 gallon is getting tight. This fish should asttain six inches body length with a vertical fin span of 8 inches. That doesn't leave much space. And if this is a male/female bonded pair, they will spawn.
Three years in a 10g may have caused serious harm to the angelfish. Let's hope not.