I just dragged your animations in each Timeline to the beginning, so they were all 1 sec in length.
Went to your Main Timeline and highlight everything and decreased the opacity to 0%.
• Deleted your opacity keyframes.
• then I placed the timeline playhead at 0 secs (frame 0) and made sure the opacity was set to 0%
• pressed record
• moved the timeline playhead to 1 sec (frame 30)
• increased the opacity to 100%
Repeated this for the other timelines (make sure the previous row is visible throughout the entire timeline)
now you should have an animation for opacity and your original scale transform animation
• Next, I moved your HTML widgets down a little, as I'm using a laptop, so when previewed you can only see the first row.
et voila ......