This is going to take a photo to clarify the situation :-)

First, woody plants/trees can't be divided in the same sense one would divide a perennial. Typically, there is only one growth point emerging from the root crown and a woody one at that - just not a divisable situation. Suckering shrubs are a bit different but still not divided like a perennial - you risk the entire plant unless you just remove a somewhat remote rooted sucker.

Named forms of Japanese maples are nearly always grafted. And the graft should be fairly obvious at close examination. You might have growth emerging from the rootstock (below the graft), which would account for the difference in appearance. Still not a dividable plant :-) But I think it is far more likely that you have a seedling grown tree - or three of them - that arose out of a simultaneous germination of three different seeds. Seedling grown J. maples can be extremely variable in appearance. I doubt this was done intentionally but although not common, it could happen naturally. If you have three separate, distinct trees growing out of the same planting hole, it IS conceivable these could be separated and "divided" provided there is no occlusion or melding of the bark from one tree to its neighbor.

But this is really all just speculation and I'd hesitate to recommend any action until you can post photos that accurately depict the sitation.

here it is what I am talking about.

Here is a link that might be useful: 3 tree in 1

closer look//

Here is a link that might be useful: closer look

Only the first of your photos was visible and that was not a clear enough view of the trunk(s) to see exactly what is going on. Can you try again showing a detail of this area and the three separate stems/trunks? I also didn't notice anything that showed an obvious difference in the color or shape of the foliage, either.

the leaves are different belive me.i am posting again the colser picture.
looks to me that if there are 3 different trees from 3 seeds I have a chance otherwise I should leave it.
I will follow your advice aethetic and dig around to take a closer look to the root system.

Here is a link that might be useful: closer2

You don't get different shaped leaves on the same tree. There me be a secondary leafing out with new growth coloring but I never have seen the leaf shape change unless it is sucker growth from beneath the graft that grafts the special JM scion (cutting) to the common JM root stock.

You probably have three different trees grouped together. You could sacrifice two and keep the more attractive tree by cutting the other two down to the ground and continuing to prune them down until they give up on putting out new growth and die. This would not do any root damage to the tree you wanted to retain.

It DOES look like three separate trunks, indicating three distinct trees. Conceivably, the combined rootball could be dug and divided, however Japanese maples have quite delicate root systems that are easily damaged by digging and handling and you run the risk of introducing wounds that could lead to diseases. I wouldn't attempt this until the tree(s) are fully dormant.

I'd be inclined to leave them alone......it/they are an attractive shape and form as-is, IMO. And I still don't see a significant difference in leaf shape and color between the three. If indeed a grouping of three seedling JM's, appearance would be variable but generally only subtly so.

FWIW, you CAN get different foliage shapes and even colors on a single tree. It is a form of reversion and/or juvenile growth and some cultivars are quite prone to it. Just saw a very nice little 'Villa Taranto' exhibiting exactly this behavior - the majority of the foliage was the very finely textured, greenish-red linearlobum foliage that is typical of this cultivar with growth at some branch ends of larger, coarser lobed leaves that were a bright red. While a little disturbing in contrast now, the foliage on these same shoots next season will be the typical VT foliage.

need again some advice as after I separate the trunks in January one of them is doing very well the other seems to strugle(the last one died but he was week anyway)
The one that strugle and I identified as glowing embers is the one that I demaged some roots and now looks to me is loosing too many buds.Do you think I sould prune now some big branches that I kept this year just to minimaze the stress??
i am thinking that pruning some branches will help the roots to support the actual crown.What do you think