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Scale can be dealt with no problem. You can use these ingredients together to try to get rid of them (though the alcohol may hurt the plant, so it is best to leave it out). Here is the proper mix: https://www.gardeningknowhow.com/problems/pests/how-to-make-white-oil-for-an-insecticide.htm

You may also want to consider neem oil. It is very effective against scale and is harmless to people and pets. You can learn more here: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm

It is not likely they survived 3 years. They normally can only stay dormant for about a year.

It might have sun scald, which is like a sunburn for plants. There is not to much you can do for the damaged leaves. They will continue to turn brown. But keep it in the shade and watered as it should be and it should regrow the leaves.

This article will help: https://www.gardeningknowhow.com/plant-problems/disease/learn-about-plant-rust-disease-and-rust-treatment.htm

This article should help: https://www.gardeningknowhow.com/ornamental/foliage/ferns/transplanting-ferns.htm

Time to transplant to a larger pot. Use a good potting soil that is rather loose. Do not be tempted to buy cheap potting soil. YOu can either gently seperate the individual plants in the pot or just transplant as is. I generally just leave them because I tend to do damage to the roots if they do not seperate easily. It will still live but goes through an ugly stage where some of the top dies off (for me, anyway).