How to?

Copy and paste using TESVSnip

Be extremely careful as there's a distinct possibility the resulting plugin will be broken. If you merge Plugin A into Plugin B or visa versa and both have forms with the same FormIDs (last six characters) you'll end up with a botched plugin that will sink like the Titanic over 'bashing' forms. We NEED TES5Edit badly... >_>

Mmmm so when I create a new item in A and a new item in B when I merge they will have the same id and overlap ?

Quite possibly. There's no guarantee the Next Expected Object IDs (NOIDs) of separate plugins won't conflict, so Plugin A's XX000D62 ARMO form could collide with Plugin B's XX000D62 that is a CELL, opening the door to all sorts of problems as the referencing forms will be baffled, trying to add a cell to the player's inventory or whatnot. A malformed plugin can conflict http://i.imgur.com/NNtpl.png.

is there another way instead of wyrebash then to merge plugins?

Not that I'm aware of. For small mergers, TESVSnip should be fine as long as you make sure, pre-merge, that the result won't be self-conflicted.

I do it in the CK. Here's the steps -

1. Select both esp files in the CK and set the biggest plugin as the active file. (see *)
2. Click OK and load up the cell of the non-active plugin.
3. Select everthing in the cell and duplicate it.
4. Cut all the duplicated objects.
5. Delete the cell (see **)
5. Create a new cell by duplicating the AAMarkers and then delete everthing in it., except Navmesh
6. Rename the duplicated cell and then open it.
7. Right click -> Paste in Place
8. Save

* If one of the cells has a lot of custom duplicated items, make that your active cell.
** Although I delete the cell, it is not deleted from the .esp file because that .esp is not the active file.

A few thing to look out for

Any duplicated objects that have been modified will not have those properties once you copy them over. That's why you pick the the cell with the most custom objects, as the active plugin.
The custom properties on objects will have to be done again. Not a big problem.
You will need to re-duplicate them.
Objects that have links will have those links broken when you Cut them. Take this into consideration. Bookshelf containers will have their links severed.

[Edit] Now that i think of it, if you copy the duplicated items, instead of cutting them, it might keep links attached. Can't really remember. It's been a while since I done it. Try it and see.

Make sure you back-up both files first

Ok I will try a test later with ur method thanks .... hope will work ...

I tried Tamb0's method but the CK crashed everytime I tried to copy the objects. I may be that my files were too big as the small one had over 5000 records. I ended up changing his method a little bit with the following steps and it worked pretty well I think.

Load the two esp files with your intended combination esp as the active file.
Duplicate the cell you want to copy in the cell window and save the combination esp.
Close the CK and reload just the combination esp as the active file.
Check in the data load window before you load the combination esp and delete the master dependancy on the other file if there is one. My copy file was an esm so you might not get the dependancy.
Once you load up you should see the original cell listed with the copy below it, but the original cell will be empty.
Delete just the original now empty cell, save and reload.
The original cell will be gone and you can rename the copy back to the original.

You will have all of the objects but you will have lost any unique custom data such npcs, packages, relationships, custom containers, etc and any unique object ids will be gone although the objects will be there. Go through the cell and rename all of the markers used in your packages and you can use TesVSnip to put back all the missing data. You can't just copy in the named objects you had with TesVSnip unless you want to go through and remove the duplicates. I just renamed the ones I needed to. I also went through and found a couple of objects had been mislocated.

This method only worked for the interior cell. The exterior cell would not duplicate so I used TesVSnip for that information as well, which is not very easy to explain. It takes some trial and error to determine what information copies correctly from one file to another in TesVSnip and to move it all into the correct groups so the file will work. Be sure to load the file in the CK everytime after using TexVSnip to reset the data and locate and remove any duplicate items.

Actually I do not want to add or take cells I want to add armors and weapons I did in another mod into my landscape mod ...

Well that is a whole different story. I would expect that TesVSnip would make short work of that. I have not worked with custom armor or weapons, so I am going to go out on a limb here. But you should be able to load up both files in TesVSnip. Find and highlight your references in the file you want to copy from. Right click on them and select copy to. It goves you a drop down Witt the other file highlighted. Select it and it copies them. Just go make sure it copied them into the right places, which it should. Very carefully be sure you save the right file and you should be done. I highly recommend your save backup copies before you open a file in TesVSnip. Not because the program is bad, but it is easy to make a mistake. At least it has been for me. I hope that helps.

the Duplicate > Cut > delete original objects > Paste in Place method works in exterior cells.

I should have tried that since my exteriors don't have nearly as many references. But that makes it easier to use TesVSnip as well. It's a useful program once you get used to its quirks.

Convert your first esp to an esm. Load the CK with your esm and associate it with version control. Now close the CK. Re-open the CK loading your esm and your esp as active. Run version control and check out the esp. Check it back in and merge it to the esm. Convert back to esp if you want to.

How I convert to esm?

Rename YourPlugin.esp to YourPlugin.ESM, open in CK as "Active", save, done.

Just renaming does the trick?

Ok I tried using TesVsnip and didn't work couse created a broken plugin that never loads due to duplicated IDs ...

As for Version control also is not usable solution apart probably for total conversion mods that do not care to create a skyrim esm ...

Is there any other solution ?

No. When the CK has it as active, it ticks the internal ESM flag to match the file extension.

If you want, link the parts and I can try to merge it with *Edit. No guarantees, but I think I can manage.

Are too big to upload yet , 200 mb etc ... are two big worldspace I need to place in the same esp now .....

Nope, you can merge into any ESM with Version Control. For the rest, what thekarithian said.

EDIT: Will also post the link here, I wrote a page in the Wiki on Version Control:

http://www.creationkit.com/Version_control