Q.Citrus Tree Feeding
What do I feed the orange tree and the grapefruit tree to ensure that the fruit is sweet? Does the same fertilizer work on peach, apricot, and nectarine?

Certified GKH Gardening Expert
This article will help:
https://www.gardeningknowhow.com/edible/fruits/citrus/fertilizing-citrus-trees-best-practices-for-citrus-fertilizing.htm
A balanced fertilizer like 10-10-10 or 20-20-20 will be fine. Follow the directions on the package when applying, simply because different manufacturers have different application directions. Most home and garden centers will carry them. If possible, find a citrus fertilizer (you should be able to find them at garden nurseries) which will also make sure that micro nutrients are supplied.