Picture 1 - Barbara: https://www.pixiv.net/en/artworks/105521975
Picture 2 - Ayaka: Not found yet
Picture 3 - Ayaka: https://www.pixiv.net/en/artworks/104599485
Picture 4 - Hu Tao: https://www.pixiv.net/en/artworks/105578533

If you know or found the remaining images, it'd be great if you can share the source link here. I tried finding it but bear no result.

You can use tools like SauceNAO.com IQDB.org to find the original source links using the full uncropped or near-uncropped artworks

You can also use tools like Google Reverse Image Search[images.google.com] and Yandex Reverse Image Search[yandex.com] to help find full uncropped image from a cropped image, which can be put into SauceNao & IQDB to find the original source links. But you'd need to disable Safe Search filter first.