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If the soil they are in has been saturated with water for a long time, they may have root rot. This article will help with that:
https://www.gardeningknowhow.com/plant-problems/disease/treating-root-rot-gardening-tips-for-housplants.htm

It may also be transplant shock. This article will help you if you suspect that:
https://www.gardeningknowhow.com/plant-problems/environmental/learn-how-to-avoid-and-repair-transplant-shock-in-plants.htm

It sounds like it may be brown rot. This article will help you determine if this is what you have:https://www.gardeningknowhow.com/edible/fruits/peach/brown-rot-fungus.htm

It sounds like you have peach borers. This article will help:
https://www.gardeningknowhow.com/edible/fruits/peach/peach-tree-borer.htm

Dormant sprays should actually be started in winter. Use dormant sprays before green tissue shows in spring buds. Use on days when the air temperature is above freezing. Use a Superior Oil spray for the first dormant spray application in mid- to late winter. Three weeks later make a second application of Superior Oil or Liquid Lime Sulfur.

When spraying trees to control peach borer pests, choose those with lindane endosufan or chlorpyrifos. Sprays should be mixed according to label instructions. They should also be applied so that it runs down the trunk and soaks into the ground around the base. Try not to spray on foliage or any fruit that may still be on the tree. The best time to spray trees is within the first or second week of July and again in late August or September.

Splitting most commonly occurs in freezing weather. If the wound is not weeping or splitting further, then you should just leave it alone to heal on its own. If the split is widening, you can try protective paper (sold at nurseries) to help hold it together while it heals. Do not cover the wound with tar or any other permanent substance as this can trap disease in the wound.

I suspect that it may be lacking iron and have chlorosis. This article will help:
https://www.gardeningknowhow.com/plant-problems/environmental/leaf-chlorosis-and-iron.htm