Q.Fruit Trees That Bloom but Fall Off
We have peach and pear trees (maybe 7 or 8 years), pomegranate and blueberry (2 years), and one mini orange tree (maybe it is tangerine) that is also old. Pear tree had fruit a couple of years ago, fruit was smaller but sweet and juicy, but we never had any fruit again after that. Peach, pomegranate and blueberry had a few flowers and had a couple of fruits, but they fell off before developing. Last year the mini orange tree bloomed and flowers fell off, except 4, which grew as big tangerines but the skin was brown and very dry, inside was ok but not very sweet. This year it has bloomed and most of the flowers fell. It is forming little fruit but it is turning brown.
Went to the nursery and they have recommended change of soil, like Miracle Grow Tree and Shrub soil, and a fungicide, insecticide (called Orchard Spray made by Bonide) for all my problems and also fertilizer called Vigoro.

Certified GKH Gardening Expert
Normally when you have blossom or fruit drop (or poor fruit formation), this can be attributed to an issue with pollination. If there are not enough natural pollinators around, the trees will have difficulty producing. This is why we sometimes have to intervene by hand pollinating. Just use a small paint brush and swirl it around the inside of the flower and repeat on all the flowers on the plant. You can encourage additional pollinators to the area as well. Here is more information: https://www.gardeningknowhow.com/garden-how-to/beneficial/insect-pollination-process.htm, https://www.gardeningknowhow.com/garden-how-to/beneficial/creating-a-pollinator-garden.htm Additionally, you may simply need to give the trees a high phosphorus fertilizer or add bone meal to the soil to encourage blooming and subsequent fruiting.