advice

Welcome. It's possible that your Quakers are screeching simply because they want attention. There could also be something that bothers them or upsets them in their environment. They could also be flock calling and waiting for a response from you.
I don't know why you were told not to put toys in the parrots' cage. It seems odd to me. Were you given an explanation?
A pellet-based diet is most often recommended for QPs. There are many brands and types available. ZuPreem Fruit Blend pellets are popular with QPs. My parrots also like Higgins InTune pellets. Roudybush and Harrison's are other good brands but tend to be more expensive. Offer a variety of vegetables, both cooked and raw (most types of beans must be cooked). Some fruit can be offered too. Cooked grains like quinoa and barley are nutritious choices, and cooked pasta is good too. Have patience when introducing new foods to your QPs since they may reject anything unfamiliar at first. Seeds should be fed sparingly and shouldn't be the focus of a parrot's diet.
All the best to you and the Quakers.