Guys do not know if I have done well but I think this is the best place, if not remove the post and apologize in advance

The question is ... is there a possibility of importing into Fallout 4 the weapons of Battlefield 4 and COD MW remastered to fallout4?

Edit: And the weapons of Rainbow Six Siege

P.D: I have seen that you are all great Modders

Maybe, I'm not a moder, but from what I see in the forums, you should have the mashes (I think that's how you spell it) and the models of the files you want.
At these times I wanted to be a great moder

I guess it's possible, but your best bet is to download the BF4 sound pack and replace the sounds in Modern Firearms before someone makes a pack.

its possible what would need to happen is you would need the meshes and textures you would need to convert the meshes from .obj to nif and broken up into respective parts receiver,stock,mag,etc the textures would need to be reworked and converted to .dds after that you would need to set it up in the creation kit for instance a handgun you would use say the deliverer as the template and make your changes from there unless you or someone you know is an animator you'll be stuck using existing animations sadly

Anything (or almost) is possible but I think it is a big job.
Even if I find the idea very interesting, I doubt, unless you find a modder completely crazy or in love with COD MW and Battlefield.

Who knows.....