What's easiest way to share/collate fullres photos with family in 2019?
This is an answer, but not the answer either of us want: no, it's not possible to do what you're looking for.
My wife and I have our own Apple IDs. We want to be able to automatically see all of each other's photos since 99% of our photos are of the same events and the same subjects (our children). We don't want to have to manually move/share photos, which means that Family Sharing Album is no good (and it also has a max photos limit).
The only way we've been able to solve this problem so far is to not use iCloud Photos at all. Instead, we have a shared Google Photos account and we both have that set to automatically upload all our photos there.
If I want to look at photos I just use the Google Photos app, and I'll see all the photos both of us took at the same event. It's a shame I can't stick to iCloud photos for this, but c'est la vie!