I don't think you can use subtitles with -vcodec copy. I use subtitles on all of my home movies but write them to a .ass (lol, yes someone thought that was a good idea) file. This is the file I use to crunch a lot of home movies into subtitled x265 format. Maybe it would help you?
#!/bin/sh for file in [email protected] ; do name=`echo $file | sed -e "s/\....$//g"` ffmpeg -i "$file" -c:v libx265 -threads 0 -s 1280x720 -vf kerndeint=thresh=10:map=0:order=0:sharp=1:twoway=0 -vf hqdn3d -sws_flags lanczos -aspect 16:9 -crf 24 -c:a aac -b:a 96k -strict -2 -filter:v subtitles="$file"\.ass "$file"\.265.mp4 -y done