firstly, i wanted to know how to coordonate a material for 2 different meshes
Secondly, i have issue with decals, when i applied it, it’s almost transparent, it appeared correctly with some light but i want it to appeared in shadow too , i tried to enable dbuffer decals but i don’t have “movable early zpass” in my settings
To get UVs aligned you really need to align them in your 3D modelling tool (Blender, 3ds Max). There are ways to align UVs in Unreal but you don’t want to make a material instance for each mesh with a different alignment. So align your meshes in Blender to have the same scale, alignment and rotation and then create ONE material in Unreal with UVs that match the alignment of the UVs in Blender. There is another post below about the same topic.
For Decals to work they need to be in the Deferred Decal material domain. Your decal also needs a translucency mask. To me it looks as if the translucency mask is not 1.0 (white) at the parts you want to be visible. There are more things to consider. Check the documentation