I don't agree with the above post, not trying to sound rude.
South American and Central American cichlids don't work like africans do. Unlike africans, these cichlids do make pairs for life, unless of course the other partner is taken out of that environment. If you had two females and a male, the male would choose a mate, and the other female would mos likely die from being smacked up from the pair. Even 3 females wouldn't work. You won't be able to tell the sex until they are 5-6 inches, sometimes 4". Get 6 young and grow them out and let them choose their own mate. You will get a lot better breeding success that way.
Also, the black ghost knife pair idea, not good. One will dominate the other, no matter how close in size they are. Most of the time (95%) a BGK won't work with another BGK. Mine did luckily, but they were only small before the heater broke. You are better trying your luck. If you REALLY want to have two, then get two, but be prepared with another tank. You will need a huge amount of sight breaks and hiding places.
The ornate bichir should be okay. The only problem being is that it isn't from amazonia. But if it's what you want, then get it, just make sure you get it small when you have the small BGK and sevs, so they don't get eaten.
Severums are voracious eaters of plants, so you will have no hope of plants in that tank, so make sure you have plenty of sunken wood, much like the Rio Orinoco has. The substrate in the amazon is white sand, so replicate that. There isn't many plants in the amazon so you are lucky there.
I hope I helped you.