Hi Christina, welcome to the forum!
Tetra are tropical fish. Goldfish are not. So they really do not belong in the same aquarium.
Tropical fish usually need the water temperature of 72~82F depend on the exact species. You need a heater for a tropical aquarium. Preferably adjustable and fully submersible.
By the way, what is the exact species of the "sucker fish"? There are many different species of fish called "sucker fish" in general. Some of them are also tropical fish, and some of them require even larger fish tank than goldfish when they are fully grown.
If your two goldfish are fancy goldfish, they need 30 gallon just by themselves.
If they are common goldfish, they need 55 gallon just by themselves.
Tetra brand foods are made of "fish meals", which are leftover fish parts after the better parts removed for other use.
Omega One flakes and New Life Spectrum pellets are the best in term of nutrition value. Omega One flakes are made of "whole salmon", and New Life Spectrum pellets are made of "whole krill".
Goldfish foods are usually different from tropical fish foods. Goldfish can actually make use of carbohydrates, and they can't eat high protein food all the time. While most tropical fish would enjoy foods with high protein and fat. So you need to get goldfish specific food just for the goldfish, while other tropical fish will eat tropical fish foods.
Silk plants should be fine. Yes, real plants are great, but it involves in a lot more work to keep them in good conditions.
Let me know if you have any questions.