Put them in flour, mixed in cake batter, they still sunk to the bottom. What can I do to make them stay throughout the cake.
Sounds like you've done this a few times, like the taste combo & can't get the fruit to stay suspended in the batter.
Don't know the physics here, but here are a couple practical suggestions:
1) make an upside down pound cake, with peaches lining a loaf pan, then invert to present, slice & serve
2) make muffins/mini pound cakes, with a small portion of batter & peaches in each. This will give you peaches distributed throughout the servings.
Somewhere I read an idea for dealing with fruit sinkage in muffins. (It may have been Stella Parks writing on Serious Eats.)
The recommendation was to put a dollop of batter not contain fruit in the the bottom of the muffin cups, and then fill the cups with the batter containing fruit. The idea is that the bit of fruitless batter in the bottom of the cup forms a "cushion" that the fruit won't sink into.
So you might set aside some of the cake batter, and add the fruit to the reminder. Put the fruitless batter in the bottom of the pan, then the batter containing the fruit.
If you try this, please report back.
First, you want the batter to be fairly thick when you use something like peaches which is going to give off juice in the baking process. Then I suggest you fill the pan with nearly all the batter first, and top it off with no more than about 1 1/2 - 2 cups of chopped peaches. Use just enough batter to cover that fruit, and kind of press it down lightly into the pan just enough to submerge it some. Hopefully that will let some of the fruit stay close to the top, while some will sink. Also arrange more fruit to the outside edges, which will set first in the baking process. You could also try using a light coat of regular cornstarch instead of flour, which might absorb better. These are probably the easiest ways, with stuff you have on hand. The other suggestion is to be sure you have well drained fruit, and coat it lightly with Clear Gel, a modified type of cornstarch which will help absorb extra moisture. Fruit tends to sink because it is heavier than the batter, and able to sink faster than the batter bakes to set it in place. It can also happen with juicier fruits, which produce extra liquid to thin the batter as it bakes.
I make a cake (from Sunset magazine) wherein you scrape all of the batter into the pan then place the cut fruit decoratively on top. (for peaches, cut in thin wedges, arrange in concentric circles; for plums, cut in halves). Sprinkle with plain or turbinado sugar or a sugar-cinnamon mixture then bake. The batter is a thick, heavy one. It's best when freshly baked. The fruit sinks in just a little.