Every Year My Fruit Trees, Lemon, Lime, Orange, Grapefruit,get Buds And Tiny Little Fruits. Many Many Of Them. Few Survive And Most fall off while fruit is very tiny. Why does this happen? what can i do to keep them on trees so they grow big into fruit?

Shoot a photo of the whole tree in the ground so I can see what you are talking about.

Have you fertilized your tree?
I'm not telling you to do that, just asking.

Have you pruned your tree?

And when do you water it, and how much??

Citrus trees only keep the fruit the tree is able to support. Your tree is being pollinated so all those flowers start to develop little fruits but the tree just can't handle that much, the excess abort.

Keep the trees always damp. Dry trees can't support as much fruit.

Fertilize 4 times a year with citrus specific fertilizer.

Size and age of trees matters.
All citrus have shallow feeder roots, 6-10 inches deep. They should be shallow watered, often. Dont forget to water in winter, they don't go dormant.
Deep water a couple times a year.

Did you have plenty of honeybees ?

Grass or anything growing within a couple feet of drip line of trees is a big no no.