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Unfortunately there is little that can be done.
It's best to pull the seedlings when they are still small.
You can girdle a tree, or even remove the tree.

If the Rose Of Sharon plant is sending up shoots from the roots, you can trim them at the soil surface.

https://www.gardeningknowhow.com/ornamental/trees/tgen/weed-trees.htm

Fall would be the best planting time.

Here is a link with some of the best varieties for your region.

https://www.gardeningknowhow.com/edible/fruits/pear/types-of-pear-trees.htm
I would also encourage you to contact your local County Extension Office.
They are a valuable source for information on the best types of trees to grow in your region.

Here is a link to find your closest office location.

https://www.gardeningknowhow.com/extension-search/

Excess nitrogen can certainly reduce the fruiting for your tree.
Unless you had an accidental exposure to the roots, a general lawn fertilizer exposure won't kill a tree.

https://www.gardeningknowhow.com/edible/fruits/pear/fertilizing-a-pear-tree.htm

Why is my Bradford tree not blooming out my neighbors trees are in full bloom

Many people are having the same problem this year. Your trees may put out a second batch of leaves, but unfortunately they probably won't bloom again. The good news is that the trees should recover and bloom again next year.

Yes, this could be due to the wind direction during the freeze. If it's not fireblight, that's the most likely explanation. Your tree may recover with time and produce leaves on that side, unless the branches are dead. Here's how to check whether individual branches are dead:
https://www.gardeningknowhow.com/ornamental/trees/tgen/tree-scratch-test.htm