Q.Get sour cherry tree to produce sweet cherries
We bought this house 12 years ago and inherited 3 mature cherry trees in the backyard. The trees produce very well in the summer but the cherries are very sour and bitter. Is there anything we can do to make them sweet or is that just the type of cherry trees they are?

There are different cultivators of Cherry Trees, Sweet or Tart.
If your not sure of the type of tree you have planted and they are tart, you likely will need to make pies or jams and jellies with the cherries.
Here is a link with more information.
https://www.gardeningknowhow.com/edible/fruits/cherry/cherry-tree-care.htm