Shared Library stopped downloading on iPhone that joined the shared library

I created a shared library (note this is different from a shared album) about 3 weeks ago and uploaded about 7000 photos and videos from my Mac Book Pro. They are all uploaded as can be seen my signing into iCloud Photos on the website. Additionally, they all downloaded to my iPhone, so they’re clearly in apples servers. I bought 2TB iCloud storage to support the content. I invited my mother and sister to the shared library with all the content, and they both joined. However, their iPhones have not downloaded the photos (my sister’s shows the shared library as empty and my mothers downloaded about 600 then stopped a few days ago). For my mom, she has left her phone plugged in overnight without low power mode, connected to WiFi, and she has 17.5 iOS. She also has plenty of storage. Still nothing. My sister has 17.4. The only thing I can think of is that they both have a full iCloud storage and plenty of local photos not backed up, and so until all the local photos are synced to iCloud, the iPhone will not pull the shared library photos. But this seems like a mistake, as Apples own documentation said that the storage for the shared library is provided by me, and I have 2 TB, so I am unsure why their photos will not download. I reached out to apple support, who told me to enable purchase sharing, which seemed unrelated to the shared library and did not resolve the issue. Please help, this album is very valuable to our family. Thank you very much