for absolute best practice if you’re doing a manual light map then yes, you should use a size like 64x64. UE4 generally does a very good job of creating lightmap unwraps though; i’ve only ever seen issues with lots of stacked overlaps. instead use the size the base colour and other maps will be. default lightmap size in ue4 is 64x64 though. that size is good for most objects.
can you upload one or all of the wall pieces? i think it might be easier for me to figure out what issues you’re having and how to solve them; particularly with the language barrier. i haven’t used blender much but i can download it later and take a stab. i do have both 3ds max and maya.
i will also try and upload some videos or images about unwrapping.