ffmpeg -loop 1 -i background.png -i video1.mp4 -i video2.mp4 -filter_complex \
"[1:v]scale=(iw/2)-20:-1[a]; \
 [2:v]scale=(iw/2)-20:-1[b]; \
 [0:v][a]overlay=10:(main_h/2)-(overlay_h/2):shortest=1[c]; \
 [c][b]overlay=main_w-overlay_w-10:(main_h/2)-(overlay_h/2)[video]" \
-map "[video]" output.mp4