How can I mask two clips on top of one at the same time?

[#1]

https://imgur.com/a/TSNmQAw

In the video, in between each wood plank, I want to have a different video between each planks. In some frames, you can see space to mask for two videos instead of one.

However, when I create a second mask, it nullifies the first mask (last picture on imgur link). I'm not sure how to create the masks and if the video stacking order in my timeline is correct or not.

[#2]

https://imgur.com/a/TSNmQAw

In the video, in between each wood plank, I want to have a different video between each planks. In some frames, you can see space to mask for two videos instead of one.

However, when I create a second mask, it nullifies the first mask (last picture on imgur link). I'm not sure how to create the masks and if the video stacking order in my timeline is correct or not.

[#3]

Hi JZhangi,

Have you tried nesting? That's how I would attack this problem. Need help with that?

Thanks,
Kevin