I think the error message says it all. If you want to stabilize 1920 x 1080 clips, you need to put them in a 1920 x 1080 sequence.
It's probably best to work in that sequence anyway.
Please note in the post that there are clips in two different settings. 1440x1080 and 1920x1080. These are different views of the same film from two different sources.
I saw that. Put them all in a 1920 x 1080 sequence. Work from there.
If you then need to stabilize some of the 1440 x 1080 clips, you'll have to nest them into their own matching sequence.
And then when you are finished stabilizing the 1920X1080 clips in a 1920X1080 sequence, you can use that sequence as a clip in the 1440X1080 sequence. It will have already been stabilized and will be quite usable in the 1440X1080 sequence. It will say it is a sequence, it will be the color of a sequence, but in the back of your mind you will remember that is was only one clip and is easily used as a clip.
Edit: Or, as stated above while I was tyoing my answer, stabilize the 1440X1080 and use that sequence as a clip in the 1920X1080 sequence.