Hi Valerie,

Thank you for contacting Ask Extension.  You have purchased a home with 2 older apple trees and you would like information about how to prune, fertilize and protect your apples without using dangerous pesticides.  You have a wonderful opportunity to harvest fresh apples.  I am sending a CSU Extension power point presentation which provides a wealth of information about growing fruit.  You have huge mature apple trees so you cannot control the climate/ microclimate and weather, the chill or growing degree days needed by your trees, the variety, or the location and soil.  If you have the same variety of apple trees you could plant a different variety to achieve good cross pollination.
You can get a soil test to see if your trees need fertilizer, prune your trees open up the crown to the sun, water your trees correctly, and thin fruit if needed.

https://cmg.extension.colostate.edu/wp-content/uploads/sites/59/2020/03/Tree-Fruit-Basics.pdf

Apples are susceptible to damage by the coddling moth.   I am sending information about how to control this pest without using chemicals.  A way to control this pest is to thin the fruit, remove and destroy all infected fruit, and practice good sanitation around the tree.

https://extension.colostate.edu/topic-areas/insects/codling-moth-control-in-home-plantings-5-613

 Here is some  information about how to prune fruit trees and pruning cuts.  If you would like to have a certified arborist come look at your trees and make recommendations, here are suggestions about how to select a licensed insured arborist. You have described your trees as huge so you may need some help to safely remove some branches.

https://www.treesaregood.org/

https://csfs.colostate.edu/wp-content/uploads/2024/01/Pruning-Cuts.pdf
 
https://extension.colostate.edu/topic-areas/yard-garden/training-and-pruning-fruit-trees-7-003/

You would like to protect your apples from the birds.  This could be difficult to accomplish if your trees are very large.  I have not found information from CSU about how to protect apples from the birds, many bird species are protected.   Perhaps if the damage is minor it could be tolerated.

Fireblight is a disease that can kill branches and the entire apple tree.  Information follows below.  Some varieties are resistant to this disease.

https://extension.colostate.edu/topic-areas/yard-garden/fire-blight-2-907/

Here is some general information that includes how to fertilize apple trees.  You may want to get a soil test done to determine if fertilizer is needed for your trees.

https://extension.colostate.edu/topic-areas/yard-garden/fertilizing-fruit-trees-7-612/

https://agsci.colostate.edu/soiltestinglab/

Apple trees require two different varieties for cross pollination and good fruit production.  If your trees are the same variety this could account for the reduced crop.  There may be another apple tree in your neighborhood which can provide some cross pollination.

https://planttalk.colostate.edu/topics/fruits/1201-apples/

Adequate irrigation for your trees is very important all year long because of our usually dry arid climate, this includes during the winter. 

" It can be difficult to look at your trees to determine if they need water.  A common method is to poke the screwdriver into the soil in several places around the tree, both inside and outside the dripline (the imaginary line at the edge of the
tree’s canopy). If the screwdriver can easily penetrate the soil to a depth of six to eight inches, there is no need to apply water. If, after watering, you cannot penetrate to a depth of six to eight inches, water again. Repeat this process until you have adequate soil moisture."

https://cmg.extension.colostate.edu/Gardennotes/657.pdf

Happy Growing,